fix: stabilize markdown notes — internal link modal, rename UI, trash integration

- Replace broken ObjectPickerModal with simple inline modal (Label+URL fields)
- Insert internal link at cursor position in textarea
- Add rename button in note editor header and note cards
- Add delete button on note cards with confirm dialog
- Integrate DeleteNote with shared trash (.verstak/trash/) via files.TrashFile()
- Remove hidden .verstak/trash/notes/ folder — notes use unified trash now
- Fix purgeTrashNode to clean file-record-based trash entries (notes/files)
- Add activity + sync ops to DeleteNote binding
- Add files.TrashFile() public method
- Update i18n keys for note.rename, note.deleteConfirm, internal link modal
- AssertContained: symlink-aware path containment check
- Update tests: shared trash, file record missing flag, collision on rename
- All go test ./... pass, frontend build passes, GUI binary built

internal/core/files/file.go

@@ -610,6 +610,14 @@ func (s *Service) trashRecord(r Record) error {
 	return err
 }
 
+// TrashFile moves a single file record's physical file to .verstak/trash/
+// and marks the record as missing=1. This is the same mechanism used by
+// deleteFileRecords, exposed as a public method for individual file trashing
+// (e.g. from notes.Delete).
+func (s *Service) TrashFile(rec *Record) error {
+	return s.trashRecord(*rec)
+}
+
 func (s *Service) deleteFileRecords(nodeID string) error {
 	records, err := s.ListByNode(nodeID)
 	if err != nil {