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/src/controllers/authController.ts

@@ -1,6 +1,6 @@
 import { Request, Response } from 'express';
 import bcrypt from 'bcrypt';
-import jwt, { SignOptions } from 'jsonwebtoken';
+import jwt from 'jsonwebtoken';
 import { mainPool } from '../config/database';
 import { config } from '../config/environment';