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/monitor/pinger.go

@@ -0,0 +1,92 @@
+package monitor
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"strings"
+	"time"
+
+	"gitea.dooplex.hu/admin/felhom-controller/internal/config"
+)
+
+// Pinger sends health check pings to a Healthchecks.io-compatible server.
+type Pinger struct {
+	baseURL    string
+	httpClient *http.Client
+	logger     *log.Logger
+	enabled    bool
+}
+
+// NewPinger creates a new Pinger from monitoring config.
+func NewPinger(cfg *config.MonitoringConfig, logger *log.Logger) *Pinger {
+	return &Pinger{
+		baseURL: strings.TrimRight(cfg.HealthchecksBase, "/"),
+		httpClient: &http.Client{
+			Timeout: 10 * time.Second,
+		},
+		logger:  logger,
+		enabled: cfg.Enabled,
+	}
+}
+
+// Ping sends a success signal with optional diagnostic body.
+func (p *Pinger) Ping(uuid string, body string) error {
+	return p.send(uuid, "", body)
+}
+
+// Fail sends a failure signal with diagnostic body.
+func (p *Pinger) Fail(uuid string, body string) error {
+	return p.send(uuid, "/fail", body)
+}
+
+// Start sends a "job started" signal (for duration tracking).
+func (p *Pinger) Start(uuid string) error {
+	return p.send(uuid, "/start", "")
+}
+
+func (p *Pinger) send(uuid, suffix, body string) error {
+	if !p.enabled {
+		return nil
+	}
+
+	if uuid == "" || strings.HasPrefix(uuid, "CHANGEME") {
+		return nil
+	}
+
+	url := fmt.Sprintf("%s/ping/%s%s", p.baseURL, uuid, suffix)
+
+	var lastErr error
+	for attempt := 0; attempt < 3; attempt++ {
+		if attempt > 0 {
+			time.Sleep(2 * time.Second)
+		}
+
+		var bodyReader io.Reader
+		if body != "" {
+			bodyReader = strings.NewReader(body)
+		}
+
+		req, err := http.NewRequest(http.MethodPost, url, bodyReader)
+		if err != nil {
+			lastErr = err
+			continue
+		}
+
+		resp, err := p.httpClient.Do(req)
+		if err != nil {
+			lastErr = err
+			continue
+		}
+		resp.Body.Close()
+
+		if resp.StatusCode >= 200 && resp.StatusCode < 300 {
+			return nil
+		}
+		lastErr = fmt.Errorf("HTTP %d", resp.StatusCode)
+	}
+
+	p.logger.Printf("[WARN] Health ping failed after 3 attempts (%s): %v", uuid, lastErr)
+	return nil // Never let ping failures affect the caller
+}