app: implement Epics 2–10

Add the full application logic on top of the Epic 1 skeleton:

Epic 2 — Authentication
- LoginDialog (AdwDialog, Blueprint template) with server URL,
  username, and password fields; emits logged-in signal on submit
- credentials.rs: store/load/clear via libsecret (password_store_sync /
  password_search_sync / password_clear_sync, v0_19 feature)
- api.rs: Api::login() parses Auth= token from ClientLogin response;
  fetch_write_token() fetches the write token
- Auto-login on startup from stored credentials; logout with
  AdwAlertDialog confirmation; login errors shown in AdwAlertDialog

Epic 3 — Article fetching
- model.rs: Article struct and ArticleObject GObject wrapper with
  unread property for list store binding
- Api::fetch_unread() deserializes Google Reader JSON, derives unread
  from categories, generates plain-text excerpt
- Sidebar uses a GtkStack with placeholder / loading / empty / error /
  list pages; AdwSpinnerPaintable while fetching; Try Again button

Epic 4 — Sidebar
- article_row.blp: composite template with feed title, date, title,
  and excerpt labels
- ArticleRow GObject subclass; binds ArticleObject, watches unread
  notify to apply .dim-label on the title; relative timestamp format

Epic 5 — Content pane
- content.html updated: setArticle(), checkKey(), feedthemonkey: URI
  navigation scheme; dark mode via prefers-color-scheme
- content.css: proper article layout, dark mode, code blocks
- WebView loaded from GResource; decide-policy intercepts
  feedthemonkey:{next,previous,open} and all external links

Epic 6 — Read state
- Api::mark_read() / mark_unread() via edit-tag endpoint
- Optimistic unread toggle on ArticleObject; background API calls;
  mark_unread_guard prevents re-marking on navigation
- AdwToast shown on mark-unread

Epic 7 — Keyboard shortcuts
- GtkShortcutController on window for all shortcuts from the backlog
- shortcuts.blp: AdwShortcutsWindow documenting all shortcuts
- F1 opens shortcuts dialog; Ctrl+W closes window; Ctrl+Q quits

Epic 8 — Zoom
- zoom_in/zoom_out/zoom_reset wired to Ctrl+±/0; zoom level saved to
  and restored from GSettings zoom-level key

Epic 9 — Window state persistence
- Window width/height/maximized saved on close, restored on open
- (Sidebar width deferred — AdwNavigationSplitView fraction binding)

Epic 10 — Polish
- AdwAboutDialog with app name, version, GPL-3.0, website
- Logout confirmation AdwAlertDialog with destructive button
- Win.toggle-fullscreen action (F11)
- Api dropped on window close to cancel in-flight requests

src/article_row.rs

@@ -0,0 +1,132 @@
+use gtk4::glib;
+use gtk4::subclass::prelude::ObjectSubclassIsExt;
+
+glib::wrapper! {
+    pub struct ArticleRow(ObjectSubclass<imp::ArticleRow>)
+        @extends gtk4::Box, gtk4::Widget,
+        @implements gtk4::Accessible, gtk4::Buildable, gtk4::ConstraintTarget, gtk4::Orientable;
+}
+
+impl ArticleRow {
+    pub fn new() -> Self {
+        glib::Object::new()
+    }
+
+    pub fn bind(&self, obj: &crate::model::ArticleObject) {
+        self.imp().bind(obj);
+    }
+
+    pub fn unbind(&self) {
+        self.imp().unbind();
+    }
+}
+
+mod imp {
+    use super::*;
+    use crate::model::ArticleObject;
+    use gtk4::prelude::*;
+    use gtk4::subclass::prelude::*;
+    use gtk4::CompositeTemplate;
+    use glib::object::ObjectExt;
+    use std::cell::RefCell;
+
+    #[derive(CompositeTemplate, Default)]
+    #[template(resource = "/net/jeena/FeedTheMonkey/ui/article_row.ui")]
+    pub struct ArticleRow {
+        #[template_child]
+        pub feed_title_label: TemplateChild<gtk4::Label>,
+        #[template_child]
+        pub date_label: TemplateChild<gtk4::Label>,
+        #[template_child]
+        pub title_label: TemplateChild<gtk4::Label>,
+        #[template_child]
+        pub excerpt_label: TemplateChild<gtk4::Label>,
+
+        pub bindings: RefCell<Vec<glib::Binding>>,
+        pub unread_handler: RefCell<Option<(ArticleObject, glib::SignalHandlerId)>>,
+    }
+
+    #[glib::object_subclass]
+    impl ObjectSubclass for ArticleRow {
+        const NAME: &'static str = "ArticleRow";
+        type Type = super::ArticleRow;
+        type ParentType = gtk4::Box;
+
+        fn class_init(klass: &mut Self::Class) {
+            klass.bind_template();
+        }
+
+        fn instance_init(obj: &glib::subclass::InitializingObject<Self>) {
+            obj.init_template();
+        }
+    }
+
+    impl ObjectImpl for ArticleRow {}
+    impl WidgetImpl for ArticleRow {}
+    impl BoxImpl for ArticleRow {}
+
+    impl ArticleRow {
+        pub fn bind(&self, obj: &ArticleObject) {
+            let article = obj.article();
+
+            self.feed_title_label.set_text(&article.feed_title);
+            self.title_label.set_text(&article.title);
+            self.excerpt_label.set_text(&article.excerpt);
+            self.date_label.set_text(&relative_time(article.published));
+
+            self.update_read_style(article.unread);
+            drop(article);
+
+            // Watch for unread state changes
+            let title_label = self.title_label.clone();
+            let id = obj.connect_notify_local(Some("unread"), move |obj, _| {
+                let unread = obj.article().unread;
+                if unread {
+                    title_label.remove_css_class("dim-label");
+                } else {
+                    title_label.add_css_class("dim-label");
+                }
+            });
+            *self.unread_handler.borrow_mut() = Some((obj.clone(), id));
+        }
+
+        pub fn unbind(&self) {
+            if let Some((obj, id)) = self.unread_handler.borrow_mut().take() {
+                obj.disconnect(id);
+            }
+            for b in self.bindings.borrow_mut().drain(..) {
+                b.unbind();
+            }
+        }
+
+        fn update_read_style(&self, unread: bool) {
+            if unread {
+                self.title_label.remove_css_class("dim-label");
+            } else {
+                self.title_label.add_css_class("dim-label");
+            }
+        }
+    }
+}
+
+fn relative_time(unix: i64) -> String {
+    let now = std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .unwrap_or_default()
+        .as_secs() as i64;
+    let diff = now - unix;
+    if diff < 60 {
+        "just now".to_string()
+    } else if diff < 3600 {
+        let m = diff / 60;
+        format!("{m}m ago")
+    } else if diff < 86400 {
+        let h = diff / 3600;
+        format!("{h}h ago")
+    } else if diff < 172800 {
+        "Yesterday".to_string()
+    } else {
+        let d = diff / 86400;
+        format!("{d}d ago")
+    }
+}