feat(telemetry): add caching, alerts, migration & dashboard improvements
- Add Redis/in-memory caching layer (cache.go)
- Add SMTP alerting for high failure rates (alerts.go)
- Add data migration script from old API (migrate.go)
- Add docker-compose.yml for easy deployment
- Move dashboard to / with redirect from /dashboard
- Add dark/light mode toggle
- Add error analysis and failed apps statistics
- Add PVE version and LXC/VM type stats
- Add /metrics Prometheus endpoint
- Add /api/records pagination endpoint
- Add CSV export functionality
- Enhanced healthcheck with PB connection status
New ENV vars:
- Cache: ENABLE_CACHE, CACHE_TTL_SECONDS, ENABLE_REDIS, REDIS_URL
- Alerts: ALERT_ENABLED, SMTP_*, ALERT_FAILURE_THRESHOLD, etc.
- Migration: RUN_MIGRATION, MIGRATION_REQUIRED, MIGRATION_SOURCE_URL
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