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.

build.rs

@@ -0,0 +1,52 @@
+use std::path::PathBuf;
+use std::process::Command;
+
+fn main() {
+    let manifest_dir = PathBuf::from(std::env::var("CARGO_MANIFEST_DIR").unwrap());
+    let data_dir = manifest_dir.join("data");
+    let ui_dir = data_dir.join("ui");
+    let out_dir = PathBuf::from(std::env::var("OUT_DIR").unwrap());
+
+    // Compile all .blp files to .ui files
+    let blp_files: Vec<_> = std::fs::read_dir(&ui_dir)
+        .expect("data/ui/ directory not found")
+        .filter_map(|e| e.ok())
+        .map(|e| e.path())
+        .filter(|p| p.extension().map_or(false, |ext| ext == "blp"))
+        .collect();
+
+    for blp in &blp_files {
+        println!("cargo:rerun-if-changed={}", blp.display());
+    }
+
+    if !blp_files.is_empty() {
+        let status = Command::new("blueprint-compiler")
+            .arg("batch-compile")
+            .arg(&ui_dir)
+            .arg(&ui_dir)
+            .args(&blp_files)
+            .status()
+            .expect("failed to run blueprint-compiler — is it installed?");
+        assert!(status.success(), "blueprint-compiler failed");
+    }
+
+    // Compile GSettings schema
+    let schema_file = data_dir.join("net.jeena.FeedTheMonkey.gschema.xml");
+    println!("cargo:rerun-if-changed={}", schema_file.display());
+
+    // Compile GResource
+    let gresource_xml = data_dir.join("resources.gresource.xml");
+    println!("cargo:rerun-if-changed={}", gresource_xml.display());
+
+    let gresource_out = out_dir.join("feedthemonkey.gresource");
+    let status = Command::new("glib-compile-resources")
+        .arg(format!("--sourcedir={}", data_dir.display()))
+        .arg(format!("--sourcedir={}", manifest_dir.display()))
+        .arg(format!("--target={}", gresource_out.display()))
+        .arg(&gresource_xml)
+        .status()
+        .expect("failed to run glib-compile-resources — is it installed?");
+    assert!(status.success(), "glib-compile-resources failed");
+
+    println!("cargo:rustc-env=GRESOURCE_FILE={}", gresource_out.display());
+}