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/backup/backup.go

@@ -414,6 +414,14 @@ func (m *Manager) SetStackProvider(provider StackDataProvider) {
 	m.stackProvider = provider
 }
 
+// GetStackHDDMounts returns HDD mount paths for the named stack via the stack provider.
+func (m *Manager) GetStackHDDMounts(name string) []string {
+	if m.stackProvider == nil {
+		return nil
+	}
+	return m.stackProvider.GetStackHDDMounts(name)
+}
+
 // resolveAppBackupPaths returns HDD paths for all enabled app backups.
 func (m *Manager) resolveAppBackupPaths() []string {
 	if m.stackProvider == nil || m.settings == nil {