refactor: remove bundled Claude Code binary support

- Remove all bundled/sidecar binary functionality
- Delete build scripts for fetching and building Claude executables
- Simplify binary detection to only support system installations
- Update UI to remove bundled installation options
- Update build configuration and documentation

.github/workflows/build-test.yml

@@ -100,7 +100,7 @@ jobs:
       - name: Build frontend
         run: bun run build
 
-      # Build Tauri application (no bundle for faster CI)
+      # Build Tauri application
       - name: Build Tauri application
         run: bun run tauri build --no-bundle -d
         env: