v0.4.0: monitoring & backup — scheduler, CPU/temp metrics, healthchecks, restic backups

Phase 2 (Monitoring & Health):
- Central job scheduler replacing ad-hoc goroutines (internal/scheduler)
- CPU usage collector via /proc/stat background sampling (internal/system/cpu_linux.go)
- Temperature reading from /sys/class/thermal + /host/sys (Docker mount)
- Load average from /proc/loadavg
- Healthchecks.io-compatible HTTP pinger (internal/monitor/pinger.go)
- System health checks: disk, memory, CPU, temp, Docker, protected containers (internal/monitor/healthcheck.go)

Phase 3 (Backups):
- Database auto-discovery via docker ps + docker inspect (internal/backup/dbdump.go)
- Database dumping via docker exec (pg_dump / mariadb-dump) with atomic writes
- Restic backup integration with auto-password generation (internal/backup/restic.go)
- Backup orchestrator: DB dumps + restic snapshots + weekly prune (internal/backup/backup.go)
- Manual backup trigger via dashboard button and POST /api/backup/run

Dashboard UI:
- CPU usage bar with load average display
- Temperature with colored indicator dot
- Backup status card with last run time, DB count, repo stats
- "Mentés most" button for manual backup trigger

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

controller/internal/system/info.go

@@ -17,4 +17,11 @@ type SystemInfo struct {
 	HDDAvailGB    float64 `json:"hdd_avail_gb,omitempty"`
 	HDDPercent    float64 `json:"hdd_percent,omitempty"`
 	HDDConfigured bool    `json:"hdd_configured"`
+
+	CPUPercent         float64 `json:"cpu_percent"`
+	LoadAvg1           float64 `json:"load_avg_1"`
+	LoadAvg5           float64 `json:"load_avg_5"`
+	LoadAvg15          float64 `json:"load_avg_15"`
+	TemperatureCelsius float64 `json:"temperature_celsius"`
+	TemperatureSource  string  `json:"temperature_source,omitempty"`
 }