feat: add release build script

- scripts/build-release.sh: builds, signs, and copies .app to dist/release/
- Bundle targets narrowed to app + dmg
- npm run release convenience script
- README documents the release build workflow

Co-authored-by: Cursor <cursoragent@cursor.com>

.gitignore

@@ -9,5 +9,6 @@ node_modules
 !.env.example
 vite.config.js.timestamp-*
 vite.config.ts.timestamp-*
+dist/
 .cursor/
 .vscode/