ui: overhaul sidebar, add content filters and state improvements

Sidebar layout:
- Replace AdwNavigationSplitView with GtkPaned for a resizable sidebar
  with a persistent width stored in GSettings.
- Apply navigation-sidebar CSS class to the content Stack only (not the
  ToolbarView) so both header bars share the same colour and height.
- Override Adwaita's automatic paned-first-child header tint and gap via
  application-level CSS.
- Remove the gap between the sidebar header and the first list item.
- Add toggle-sidebar button and F9 shortcut; sidebar visibility and width
  are persisted across restarts.

Loading indicator:
- Replace the large AdwSpinner status page + header Stack with a small
  Gtk.Spinner (16×16) in the header Stack so the header height never
  changes during loading.

Article row:
- Add hexpand to title and excerpt labels so text reflows when the
  sidebar is resized.

Content:
- Inline CSS into the HTML template at load time (/*INJECT_CSS*/
  placeholder) so WebKit does not need a custom URI scheme handler.
- Fix max-width centering and padding for article body and header.
- Fix embedded video/iframe auto-opening in browser by checking
  NavigationType::LinkClicked instead of is_user_gesture().

Content filters:
- Add Preferences dialog with a TextView for content-rewrite rules
  stored in GSettings (content-filters key).
- Rule format: "domain find replace [find replace …]" one per line.
- Rules are applied to article HTML before display and reloaded on
  every refresh.

Shortcuts:
- Add Ctrl+W to close, Ctrl+Q to quit, F1 for keyboard shortcuts
  overlay, j/k and arrow-key navigation via a capture-phase controller
  so keys work regardless of which widget has focus.

Misc:
- Set window title to "FeedTheMonkey" (fixes Hyprland title bar).
- Update About dialog website URL.

src/app.rs

@@ -51,6 +51,33 @@ mod imp {
                 .expect("failed to load GResource");
             gio::resources_register(&resource);
 
+            // Apply application-level CSS tweaks
+            let css = gtk4::CssProvider::new();
+            css.load_from_string(
+                "paned > :first-child .top-bar headerbar {
+                    background-color: @headerbar_bg_color;
+                    box-shadow: none;
+                }
+                paned > :first-child > toolbarview > .content {
+                    padding-top: 0;
+                    margin-top: 0;
+                }
+                .sidebar-content row:not(:selected) {
+                    background-color: alpha(@window_fg_color, 0.07);
+                }
+                .sidebar-content row:not(:selected):hover {
+                    background-color: alpha(@window_fg_color, 0.14);
+                }
+                .sidebar-content row:selected {
+                    background-color: alpha(@window_fg_color, 0.22);
+                }"
+            );
+            gtk4::style_context_add_provider_for_display(
+                &gtk4::gdk::Display::default().unwrap(),
+                &css,
+                gtk4::STYLE_PROVIDER_PRIORITY_APPLICATION,
+            );
+
             let window = FeedTheMonkeyWindow::new(app.upcast_ref());
 
             // Shortcuts overlay
@@ -74,7 +101,7 @@ mod imp {
                         .version("3.0.0")
                         .copyright("© Jeena Paradies")
                         .license_type(gtk4::License::Gpl30)
-                        .website("https://github.com/jeena/FeedTheMonkey")
+                        .website("https://git.jeena.net/jeena/FeedTheMonkey")
                         .developer_name("Jeena Paradies")
                         .build();
                     dialog.present(win.as_ref().map(|w| w.upcast_ref::<gtk4::Widget>()));
@@ -116,10 +143,8 @@ fn setup_shortcuts(window: &FeedTheMonkeyWindow) {
         controller.add_shortcut(shortcut);
     };
 
-    add(&controller, Key::j,      ModifierType::empty(),       "win.next-article");
-    add(&controller, Key::Right,  ModifierType::empty(),       "win.next-article");
-    add(&controller, Key::k,      ModifierType::empty(),       "win.prev-article");
-    add(&controller, Key::Left,   ModifierType::empty(),       "win.prev-article");
+    // j/k/Left/Right are handled by a capture-phase key controller in window.rs
+    // so they work regardless of which widget has focus.
     add(&controller, Key::r,      ModifierType::empty(),       "win.reload");
     add(&controller, Key::u,      ModifierType::empty(),       "win.mark-unread");
     add(&controller, Key::Return, ModifierType::empty(),       "win.open-in-browser");
@@ -128,6 +153,7 @@ fn setup_shortcuts(window: &FeedTheMonkeyWindow) {
     add(&controller, Key::equal,  ModifierType::CONTROL_MASK,  "win.zoom-in");
     add(&controller, Key::minus,  ModifierType::CONTROL_MASK,  "win.zoom-out");
     add(&controller, Key::_0,     ModifierType::CONTROL_MASK,  "win.zoom-reset");
+    add(&controller, Key::F9,     ModifierType::empty(),       "win.toggle-sidebar");
     add(&controller, Key::F11,    ModifierType::empty(),       "win.toggle-fullscreen");
     add(&controller, Key::w,      ModifierType::CONTROL_MASK,  "window.close");
     add(&controller, Key::q,      ModifierType::CONTROL_MASK,  "app.quit");

src/filters.rs

@@ -0,0 +1,68 @@
+/// Content rewrite rules stored in GSettings key "content-filters".
+///
+/// Format — one rule per line, tokens separated by spaces:
+///
+///   domain  from  to  [from  to  …]
+///
+/// Examples:
+///
+///   www.imycomic.com  -150x150.jpg  .jpg
+///   www.stuttmann-karikaturen.de  /thumbs/  /
+///   existentialcomics.com  src="//static  src="https://static
+///
+/// The domain is matched as a substring of the article's GUID and link URL.
+/// Blank lines and lines starting with # are ignored.
+
+use gtk4::gio;
+use gtk4::prelude::SettingsExt;
+
+pub struct Rule {
+    pub pattern: String,
+    pub replacements: Vec<(String, String)>,
+}
+
+/// Parse the multi-line text from the GSettings key into rules.
+pub fn parse(text: &str) -> Vec<Rule> {
+    let mut rules = Vec::new();
+    for line in text.lines() {
+        let line = line.trim();
+        if line.is_empty() || line.starts_with('#') {
+            continue;
+        }
+        let tokens: Vec<&str> = line.splitn(usize::MAX, ' ')
+            .map(str::trim)
+            .filter(|t| !t.is_empty())
+            .collect();
+        if tokens.len() < 3 || tokens.len() % 2 == 0 {
+            // Need: domain + at least one from/to pair (odd total ≥ 3)
+            eprintln!("filters: skipping malformed line: {line}");
+            continue;
+        }
+        let pattern = tokens[0].to_string();
+        let replacements = tokens[1..]
+            .chunks(2)
+            .map(|c| (c[0].to_string(), c[1].to_string()))
+            .collect();
+        rules.push(Rule { pattern, replacements });
+    }
+    rules
+}
+
+/// Load rules from GSettings.
+pub fn load_rules() -> Vec<Rule> {
+    let settings = gio::Settings::new("net.jeena.FeedTheMonkey");
+    parse(&settings.string("content-filters"))
+}
+
+/// Apply all matching rules to `content`.
+pub fn apply(rules: &[Rule], guid: &str, link: &str, content: &str) -> String {
+    let mut out = content.to_string();
+    for rule in rules {
+        if guid.contains(&rule.pattern) || link.contains(&rule.pattern) {
+            for (from, to) in &rule.replacements {
+                out = out.replace(from.as_str(), to.as_str());
+            }
+        }
+    }
+    out
+}

src/preferences_dialog.rs

@@ -0,0 +1,75 @@
+use gtk4::prelude::*;
+use gtk4::subclass::prelude::*;
+use gtk4::{gio, glib};
+
+glib::wrapper! {
+    pub struct PreferencesDialog(ObjectSubclass<imp::PreferencesDialog>)
+        @extends libadwaita::Dialog, gtk4::Widget,
+        @implements gtk4::Accessible, gtk4::Buildable, gtk4::ConstraintTarget;
+}
+
+impl PreferencesDialog {
+    pub fn new() -> Self {
+        glib::Object::builder().build()
+    }
+}
+
+pub mod imp {
+    use super::*;
+    use gtk4::CompositeTemplate;
+    use libadwaita::subclass::prelude::*;
+
+    #[derive(CompositeTemplate, Default)]
+    #[template(resource = "/net/jeena/FeedTheMonkey/ui/preferences_dialog.ui")]
+    pub struct PreferencesDialog {
+        #[template_child]
+        pub filters_text_view: TemplateChild<gtk4::TextView>,
+    }
+
+    #[glib::object_subclass]
+    impl ObjectSubclass for PreferencesDialog {
+        const NAME: &'static str = "PreferencesDialog";
+        type Type = super::PreferencesDialog;
+        type ParentType = libadwaita::Dialog;
+
+        fn class_init(klass: &mut Self::Class) {
+            klass.bind_template();
+        }
+
+        fn instance_init(obj: &glib::subclass::InitializingObject<Self>) {
+            obj.init_template();
+        }
+    }
+
+    impl ObjectImpl for PreferencesDialog {
+        fn constructed(&self) {
+            self.parent_constructed();
+            self.load();
+            // Save on every text change
+            let obj_weak = self.obj().downgrade();
+            self.filters_text_view.buffer().connect_changed(move |_| {
+                if let Some(obj) = obj_weak.upgrade() {
+                    obj.imp().save();
+                }
+            });
+        }
+    }
+
+    impl PreferencesDialog {
+        fn load(&self) {
+            let settings = gio::Settings::new("net.jeena.FeedTheMonkey");
+            let text = settings.string("content-filters");
+            self.filters_text_view.buffer().set_text(&text);
+        }
+
+        fn save(&self) {
+            let buf = self.filters_text_view.buffer();
+            let text = buf.text(&buf.start_iter(), &buf.end_iter(), false);
+            let settings = gio::Settings::new("net.jeena.FeedTheMonkey");
+            settings.set_string("content-filters", &text).ok();
+        }
+    }
+
+    impl WidgetImpl for PreferencesDialog {}
+    impl AdwDialogImpl for PreferencesDialog {}
+}