Add Gitea integration + ESLint setup

Phase 3: Gitea Integration
- Migration 012: app_settings table + gitea_commit_sha on endpoint_versions
- SettingsService: encrypted token storage (AES-256-GCM from JWT_SECRET)
- GiteaService: full REST API client — repo management, file CRUD,
  branches, commit history, diff/compare, pull requests, sync all
- giteaController + routes: 15 API endpoints for settings, branches,
  commits, PRs, endpoint info, sync
- VersionService hooks: auto-sync to Gitea on publish/draft (non-blocking)
- Frontend: Gitea tab in Settings (connection, sync status, branch mgmt),
  Gitea panel in EndpointEditor (file link, last commit SHA)
- docker-compose.gitea.yml: optional companion Gitea container
- Cache fix: index.html served with no-cache for instant deploys

ESLint Setup
- Backend: eslint 8 + @typescript-eslint configured
- Frontend: eslint 8 + @typescript-eslint + react-hooks + react-refresh
- Fixed 15 lint issues: unused imports, require statements, escapes,
  Function type, empty catch blocks
- Added npm run lint / lint:fix scripts

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/package.json

@@ -42,6 +42,9 @@
     "@types/swagger-jsdoc": "^6.0.4",
     "@types/swagger-ui-express": "^4.1.6",
     "@types/uuid": "^9.0.7",
+    "@typescript-eslint/eslint-plugin": "^6.21.0",
+    "@typescript-eslint/parser": "^6.21.0",
+    "eslint": "^8.57.1",
     "http-proxy-middleware": "^3.0.5",
     "nodemon": "^3.0.2",
     "ts-node": "^10.9.2",