Switch to Netlify adapter with GitHub API persistence

- Swap @astrojs/node for @astrojs/netlify adapter
- Admin API reads/writes admin-data.json via GitHub API in production
- Status changes (commitStatus) and deletes commit directly to repo
- Env vars: ADMIN_PASSWORD, GITHUB_TOKEN
- Local dev falls back to filesystem (no env vars needed)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -28,3 +28,6 @@ Thumbs.db
 bun.lockb
 yarn.lock
 pnpm-lock.yaml
+
+# Local Netlify folder
+.netlify