feat(macos): add code signing and notarization support

Add macOS code signing and notarization for Gatekeeper compatibility:

- Add hardened runtime configuration in package.json
- Add entitlements.mac.plist for required app permissions
- Enable built-in electron-builder notarization
- Add code signing and notarization secrets to workflow

Required GitHub Secrets:
- CSC_LINK: Base64-encoded .p12 certificate file
- CSC_KEY_PASSWORD: Password for the .p12 certificate
- APPLE_ID: Apple Developer account email
- APPLE_APP_SPECIFIC_PASSWORD: App-specific password from appleid.apple.com
- APPLE_TEAM_ID: 10-character Apple Developer Team ID

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.github/workflows/release.yml

@@ -38,6 +38,14 @@ jobs:
       - run: npm ci
 
       - name: Build macOS Packages
+        env:
+          # Code signing
+          CSC_LINK: ${{ secrets.CSC_LINK }}
+          CSC_KEY_PASSWORD: ${{ secrets.CSC_KEY_PASSWORD }}
+          # Notarization
+          APPLE_ID: ${{ secrets.APPLE_ID }}
+          APPLE_APP_SPECIFIC_PASSWORD: ${{ secrets.APPLE_APP_SPECIFIC_PASSWORD }}
+          APPLE_TEAM_ID: ${{ secrets.APPLE_TEAM_ID }}
         run: npx electron-builder --mac --publish never
       - uses: actions/upload-artifact@v4
         with:
@@ -45,6 +53,7 @@ jobs:
           path: |
             dist/*.dmg
             dist/*.zip
+            dist/*.blockmap
             dist/latest-mac.yml
 
   build-linux: