feat: migrate to DragonflyDB and clean up environment configuration

- Replace Redis with DragonflyDB for better performance and memory efficiency
- Remove redundant environment variables (POSTGRES_*, ENCRYPTION_KEY, OAUTH_SERVICE_URL)
- Consolidate database configuration to use single DB_* variables
- Use JWT_SECRET for both JWT tokens and encryption
- Remove PORT variable redundancy, use BACKEND_PORT consistently
- Clean up docker-compose configurations for dev/prod consistency
- Add DragonflyDB configuration with optimized memory usage
- Remove redis.conf as it's no longer needed
- Update health checks to use Redis-compatible CLI for DragonflyDB
- Add missing VITE_API_URL to production frontend
- Fix GitHub Actions to use correct go.sum path
- Clean up development directories and unused files

docs/GITHUB_OAUTH_SETUP.md

@@ -117,3 +117,31 @@ GIN_MODE=debug
 ```
 
 This will provide detailed logs for troubleshooting OAuth flow issues.
+
+## 9. GitHub App Backup Setup (Optional)
+
+If you want users to install Trackeep on org/repositories and back up selected repos locally, configure a GitHub App in addition to OAuth:
+
+1. GitHub Settings → Developer settings → GitHub Apps → New GitHub App
+2. Configure:
+   - **App name**: `Trackeep`
+   - **Homepage URL**: your frontend URL
+   - **Setup URL**: `http://localhost:9000/api/v1/github/app/callback` (or your production backend URL)
+3. Add to `.env`:
+
+```bash
+GITHUB_APP_SLUG=trackeep
+GITHUB_APP_ID=123456
+GITHUB_APP_PRIVATE_KEY="-----BEGIN RSA PRIVATE KEY-----\n...\n-----END RSA PRIVATE KEY-----"
+GITHUB_BACKUP_ROOT=./data/github-backups
+GITHUB_BACKUP_TIMEOUT=10m
+```
+
+New API endpoints:
+
+- `GET /api/v1/github/app/status`
+- `GET /api/v1/github/app/install-url`
+- `GET /api/v1/github/app/callback`
+- `GET /api/v1/github/app/repos`
+- `GET /api/v1/github/backups`
+- `POST /api/v1/github/backups`