v0.12.0 — Backup page overhaul: unified app rows, bug fixes, sequential chaining

Bug fixes:
- GetFullStatus() returns deep copy; CrossDriveSummary/UnconfiguredApps/CrossDriveWarnings
  are always nil in the copy so the handler builds them fresh (fixes duplicate-apps bug)
- Replace binary IsMountPoint check with tiered CheckBackupDestination() — path-not-exist,
  not-writable, system-drive (warning), disk >90-95% full; shown as warning vs critical
- Remove dead settingsAppBackupHandler / POST /settings/app-backup route (toggle wrote
  to settings.json but nothing consumed the flag)

Architecture:
- Unified per-app backup rows: new AppBackupRow struct + buildAppBackupRows() replaces
  the two old sections with expandable rows showing all 3 layers per app
- Sequential backup chaining: cross-drive runs immediately after restic (removed
  independent cross-drive-daily/cross-drive-weekly scheduler jobs)
- Deploy page: remove "Csak kézi indítás" schedule option; add weekly consistency note

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

controller/internal/system/mounts_other.go

@@ -57,3 +57,26 @@ type FSInfo struct {
 
 // GetFSInfo returns nil on non-Linux.
 func GetFSInfo(_ string) *FSInfo { return nil }
+
+// DestinationHealth holds the result of a tiered backup destination check.
+type DestinationHealth struct {
+	Exists      bool
+	Writable    bool
+	MountPoint  bool
+	SystemDrive bool
+	UsedPercent float64
+	FreeGB      float64
+	Warning     string
+	Blocked     bool
+	Severity    string
+}
+
+// CheckBackupDestination always returns ok on non-Linux (assume healthy for dev/testing).
+func CheckBackupDestination(path string) DestinationHealth {
+	return DestinationHealth{
+		Exists:     true,
+		Writable:   true,
+		MountPoint: true,
+		Severity:   "ok",
+	}
+}