Phase C: package as an unsigned macOS .dmg (electron-builder)

Adds shareable desktop packaging so the app can be handed to teammates.

- electron-builder@25 + electron-builder.yml: appId io.stephenmann.commitea,
  productName CommiTea, icon from the logo (build/icon.png, 1024²), macOS dmg
  targets for arm64 + x64. Ships only out/** (electron-vite already bundles
  renderer/preload/main with core + react inlined), npmRebuild off,
  electronVersion pinned to 34.5.8 (workspace hoisting defeats auto-detect).
- Unsigned by decision: mac.identity null, hardenedRuntime off. electron-builder
  ad-hoc signs so arm64 runs; not notarized — teammates right-click → Open once.
- Scripts: `yarn pack` (--dir sanity build), `yarn dist` (both dmgs). package.json
  gains version/author/description (required by electron-builder).
- README.md: dev/build/package commands + the Gatekeeper install step.

Verified: packaged arm64 app boots from a fresh profile (lands on onboarding);
`yarn dist` produced CommiTea-0.1.0-arm64.dmg (98M) and CommiTea-0.1.0.dmg (x64,
102M), each mounting with a drag-to-Applications layout.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/desktop/package.json

@@ -1,5 +1,8 @@
 {
   "name": "@commitea/desktop",
+  "version": "0.1.0",
+  "description": "CommiTea — an AI project manager for Gitea",
+  "author": "CommiTea",
   "private": true,
   "type": "module",
   "main": "./out/main/index.js",
@@ -10,7 +13,9 @@
     "typecheck": "tsc --noEmit",
     "e2e": "electron-vite build && playwright test",
     "e2e:only": "playwright test",
-    "e2e:report": "playwright show-report e2e/.artifacts/report"
+    "e2e:report": "playwright show-report e2e/.artifacts/report",
+    "pack": "electron-vite build && electron-builder --dir",
+    "dist": "electron-vite build && electron-builder --mac"
   },
   "dependencies": {
     "@commitea/core": "workspace:*",
@@ -25,6 +30,7 @@
     "@vitejs/plugin-react": "^4.3.4",
     "autoprefixer": "^10.4.20",
     "electron": "^34.0.0",
+    "electron-builder": "^25",
     "electron-vite": "^3.1.0",
     "postcss": "^8.5.1",
     "tailwindcss": "^3.4.17",