scaffold: Epic 1 — project scaffold

Add the full Rust + GTK4 + libadwaita project skeleton:
- Cargo.toml with all dependencies (gtk4 0.11, libadwaita 0.9,
  webkit6 0.6, reqwest, serde, tokio, libsecret)
- build.rs that compiles Blueprint .blp files and bundles a GResource
- data/ui/window.blp — AdwApplicationWindow with AdwNavigationSplitView,
  sidebar with refresh button/spinner and primary menu,
  content page with article menu
- data/resources.gresource.xml bundling UI, HTML, and CSS
- data/net.jeena.FeedTheMonkey.gschema.xml with all GSettings keys
- html/content.html and html/content.css (minimal placeholders)
- src/main.rs, src/app.rs — AdwApplication with APP_ID net.jeena.FeedTheMonkey
- src/window.rs — AdwApplicationWindow GObject subclass loading the
  Blueprint template and persisting window size in GSettings
- COPYING (GPL-3.0) restored from master

The app compiles and the binary is ready to open a blank window.

data/ui/window.blp

@@ -0,0 +1,108 @@
+using Gtk 4.0;
+using Adw 1;
+
+template $FeedTheMonkeyWindow : Adw.ApplicationWindow {
+  default-width: 900;
+  default-height: 600;
+
+  Adw.ToastOverlay toast_overlay {
+    Adw.NavigationSplitView split_view {
+      sidebar: Adw.NavigationPage {
+        title: _("FeedTheMonkey");
+
+        Adw.ToolbarView {
+          [top]
+          Adw.HeaderBar {
+            [start]
+            Stack refresh_stack {
+              StackPage {
+                name: "button";
+                child: Button refresh_button {
+                  icon-name: "view-refresh-symbolic";
+                  tooltip-text: _("Refresh");
+                  action-name: "win.reload";
+                };
+              }
+
+              StackPage {
+                name: "spinner";
+                child: Adw.Spinner {};
+              }
+            }
+
+            [end]
+            MenuButton menu_button {
+              icon-name: "open-menu-symbolic";
+              primary: true;
+              menu-model: primary_menu;
+            }
+          }
+
+          Adw.StatusPage placeholder_page {
+            icon-name: "rss-symbolic";
+            title: _("FeedTheMonkey");
+            description: _("Log in to load your articles");
+          }
+        }
+      };
+
+      content: Adw.NavigationPage content_page {
+        title: _("FeedTheMonkey");
+
+        Adw.ToolbarView {
+          top-bar-style: raised;
+
+          [top]
+          Adw.HeaderBar {
+            [end]
+            MenuButton article_menu_button {
+              icon-name: "view-more-symbolic";
+              menu-model: article_menu;
+              visible: false;
+            }
+          }
+
+          Adw.StatusPage {
+            icon-name: "document-open-symbolic";
+            title: _("No Article Selected");
+          }
+        }
+      };
+    }
+  }
+}
+
+menu primary_menu {
+  section {
+    item {
+      label: _("Log Out");
+      action: "win.logout";
+    }
+  }
+
+  section {
+    item {
+      label: _("Keyboard Shortcuts");
+      action: "win.show-help-overlay";
+    }
+
+    item {
+      label: _("About FeedTheMonkey");
+      action: "app.about";
+    }
+  }
+}
+
+menu article_menu {
+  section {
+    item {
+      label: _("Mark Unread");
+      action: "win.mark-unread";
+    }
+
+    item {
+      label: _("Open in Browser");
+      action: "win.open-in-browser";
+    }
+  }
+}