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>

package.json

@@ -9,7 +9,8 @@
     "preview": "vite preview",
     "test": "vitest run",
     "check": "svelte-check --tsconfig ./tsconfig.json",
-    "tauri": "tauri"
+    "tauri": "tauri",
+    "release": "bash scripts/build-release.sh"
   },
   "license": "MIT",
   "dependencies": {