v0.9.0: Storage paths registry, per-app HDD_PATH resolution, storage management UI

- Fix backup toggles not appearing (read each app's own HDD_PATH from app.yaml)
- Storage paths registry in settings.json with auto-discovery from deployed apps
- Settings page "Adattárolók" section with disk usage, add/remove/default/schedulable
- Deploy page path field as dropdown of registered storage paths
- Health check storage monitoring (mount point, disk usage alerts)
- Mount-point validation utilities (Linux syscall + cross-platform stubs)
- Controller docker-compose mount changed to /mnt:/mnt:rw for multi-storage

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

controller/internal/report/builder.go

@@ -10,6 +10,7 @@ import (
 	"gitea.dooplex.hu/admin/felhom-controller/internal/metrics"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/monitor"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/scheduler"
+	"gitea.dooplex.hu/admin/felhom-controller/internal/settings"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/stacks"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/system"
 )
@@ -22,6 +23,7 @@ func BuildReport(
 	cpuCollector *system.CPUCollector,
 	metricsStore *metrics.MetricsStore,
 	version string,
+	storagePaths []settings.StoragePath,
 ) *Report {
 	r := &Report{
 		Version:           1,
@@ -33,7 +35,11 @@ func BuildReport(
 
 	// System info
 	staticInfo := metrics.GetStaticInfo()
-	sysInfo := system.GetInfo(cfg.Paths.HDDPath, cpuCollector)
+	hddPath := cfg.Paths.HDDPath
+	if len(storagePaths) > 0 {
+		hddPath = storagePaths[0].Path
+	}
+	sysInfo := system.GetInfo(hddPath, cpuCollector)
 
 	r.System = SystemReport{
 		Hostname:           staticInfo.Hostname,
@@ -72,7 +78,7 @@ func BuildReport(
 	r.Backup = buildBackupReport(cfg, backupMgr)
 
 	// Health
-	healthReport := monitor.RunHealthCheck(cfg, cpuCollector)
+	healthReport := monitor.RunHealthCheck(cfg, cpuCollector, storagePaths)
 	r.Health = HealthReport{
 		Status:   healthReport.Status,
 		Issues:   healthReport.Issues,