v0.12.2: restore section simplification — snapshot filtering, auto-stop/restart, UI cleanup

- StackDataProvider interface extended with StopStack/StartStack
- backup.Manager.GetStackHDDMounts() delegates to stackProvider
- RestoreApp() auto-stops app before restic restore, restarts after (even on failure)
- stackAdapter in main.go wires StopStack/StartStack through to stacks.Manager
- GET /api/backup/snapshots?stack={name} filters snapshots by app HDD paths via filterSnapshotsByPaths()
- Restore section simplified: no path list, per-app filtered snapshots, human-friendly timestamp format, single calm warning, empty-result inline message

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

controller/internal/api/router.go

@@ -445,7 +445,7 @@ func (r *Router) triggerBackup(w http.ResponseWriter, _ *http.Request) {
 	writeJSON(w, http.StatusOK, apiResponse{OK: true, Message: "Mentés elindítva"})
 }
 
-func (r *Router) backupSnapshots(w http.ResponseWriter, _ *http.Request) {
+func (r *Router) backupSnapshots(w http.ResponseWriter, req *http.Request) {
 	if r.backupMgr == nil {
 		writeJSON(w, http.StatusOK, apiResponse{OK: true, Data: []interface{}{}})
 		return
@@ -456,12 +456,39 @@ func (r *Router) backupSnapshots(w http.ResponseWriter, _ *http.Request) {
 		writeJSON(w, http.StatusInternalServerError, apiResponse{OK: false, Error: err.Error()})
 		return
 	}
+
+	// Filter by stack if requested — only return snapshots that include the app's HDD paths.
+	if stackName := req.URL.Query().Get("stack"); stackName != "" {
+		mounts := r.backupMgr.GetStackHDDMounts(stackName)
+		if len(mounts) > 0 {
+			snapshots = filterSnapshotsByPaths(snapshots, mounts)
+		}
+	}
+
 	if snapshots == nil {
 		snapshots = []backup.SnapshotInfo{}
 	}
 	writeJSON(w, http.StatusOK, apiResponse{OK: true, Data: snapshots})
 }
 
+// filterSnapshotsByPaths returns only snapshots whose Paths overlap with requiredPaths.
+// A snapshot matches if any of its paths is a prefix of (or prefixed by) any required path.
+func filterSnapshotsByPaths(snapshots []backup.SnapshotInfo, requiredPaths []string) []backup.SnapshotInfo {
+	var filtered []backup.SnapshotInfo
+outer:
+	for _, snap := range snapshots {
+		for _, required := range requiredPaths {
+			for _, sp := range snap.Paths {
+				if strings.HasPrefix(required, sp) || strings.HasPrefix(sp, required) {
+					filtered = append(filtered, snap)
+					continue outer
+				}
+			}
+		}
+	}
+	return filtered
+}
+
 // --- Metrics handlers ---
 
 func (r *Router) metricsSystem(w http.ResponseWriter, req *http.Request) {