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/.eslintrc.cjs

@@ -0,0 +1,21 @@
+module.exports = {
+  root: true,
+  env: { node: true, es2020: true },
+  extends: [
+    'eslint:recommended',
+    'plugin:@typescript-eslint/recommended',
+  ],
+  ignorePatterns: ['dist', '.eslintrc.cjs'],
+  parser: '@typescript-eslint/parser',
+  parserOptions: {
+    ecmaVersion: 2020,
+    sourceType: 'module',
+  },
+  rules: {
+    '@typescript-eslint/no-explicit-any': 'off',
+    '@typescript-eslint/no-unused-vars': ['warn', { argsIgnorePattern: '^_', varsIgnorePattern: '^_' }],
+    'no-console': 'off',
+    'prefer-const': 'warn',
+    '@typescript-eslint/no-require-imports': 'off',
+  },
+};