fix: Tier2 backup status now detects drives removed from storage (not just disconnected)

Previously, removing a storage drive from the controller only marked it as
disconnected if the StoragePath entry still existed with Disconnected:true.
Drives removed entirely from storage_paths were invisible to the check,
causing Tier2 backup UI to show green "Sikeres" and scheduler to attempt
backups to a no-longer-managed destination.

New IsStoragePathKnown() method covers both cases. UI shows yellow
"Cél meghajtó leválasztva" and scheduler skips silently.

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

controller/internal/settings/settings.go

@@ -693,6 +693,20 @@ func (s *Settings) GetConnectedPaths() []StoragePath {
 	return result
 }
 
+// IsStoragePathKnown returns whether a path belongs to any registered storage path
+// (connected, disconnected, or decommissioned). A path removed entirely from
+// storage_paths is NOT known.
+func (s *Settings) IsStoragePathKnown(path string) bool {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	for _, sp := range s.StoragePaths {
+		if path == sp.Path || strings.HasPrefix(path, sp.Path+"/") {
+			return true
+		}
+	}
+	return false
+}
+
 // GetStoppedStacks returns the list of stacks that were auto-stopped for a storage path.
 func (s *Settings) GetStoppedStacks(path string) []string {
 	s.mu.RLock()