Fix Rust build errors: use setup hook for window icon, enable image-png feature

The previous approach used Builder::default_window_icon() which doesn't
exist in Tauri 2.10. Instead, set the icon via window.set_icon() in the
setup hook, and enable the "image-png" feature flag so Image::from_bytes
can decode the PNG icon at runtime.

Also change bundle identifier from "com.triple-c.app" to
"com.triple-c.desktop" to avoid conflicting with the .app bundle
extension on macOS.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/src/test/icon-config.test.ts

@@ -5,12 +5,17 @@ import { resolve } from "path";
 describe("Window icon configuration", () => {
   const srcTauriDir = resolve(__dirname, "../../src-tauri");
 
-  it("lib.rs sets default_window_icon using the app icon", () => {
+  it("lib.rs sets window icon using set_icon in setup hook", () => {
     const libRs = readFileSync(resolve(srcTauriDir, "src/lib.rs"), "utf-8");
-    expect(libRs).toContain("default_window_icon");
+    expect(libRs).toContain("set_icon");
     expect(libRs).toContain("icon.png");
   });
 
+  it("Cargo.toml enables image-png feature for icon loading", () => {
+    const cargoToml = readFileSync(resolve(srcTauriDir, "Cargo.toml"), "utf-8");
+    expect(cargoToml).toContain("image-png");
+  });
+
   it("icon.png exists in the icons directory", () => {
     const iconPath = resolve(srcTauriDir, "icons/icon.png");
     expect(existsSync(iconPath)).toBe(true);