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/docker-compose.yml

@@ -11,20 +11,20 @@ services:
     ports:
       - "8080:8080"
     volumes:
-      # Docker socket — required for compose operations
+      # Docker socket — required for compose operations + DB dumps (docker exec)
       - /var/run/docker.sock:/var/run/docker.sock:ro
       # Controller config
       - /opt/docker/felhom-controller/controller.yaml:/opt/docker/felhom-controller/controller.yaml:ro
-      # Controller persistent data (sessions, state)
+      # Controller persistent data (sessions, restic cache, restic password)
       - controller-data:/opt/docker/felhom-controller/data
       # Stack compose files (read + write for git sync)
       - /opt/docker/stacks:/opt/docker/stacks
-      # Backup directories
+      # Backup directories (restic repo + db dumps)
       - /srv/backups:/srv/backups
-      # Restic password file
-      - /opt/docker/felhom-controller/restic-password:/opt/docker/felhom-controller/restic-password:ro
-      # HDD mount (if available, for backup paths)
+      # HDD mount (if available, for monitoring disk usage)
       - ${HDD_PATH:-/mnt/hdd_placeholder}:${HDD_PATH:-/mnt/hdd_placeholder}:ro
+      # Host /sys — for CPU temperature reading (read-only)
+      - /sys:/host/sys:ro
     environment:
       - TZ=Europe/Budapest
     labels: