notes: user-defined folders with drag-drop (task #413)

DB
- New `note_folders` table (per-user unique name); `notes.folder_id` nullable
  with `ON DELETE SET NULL` so deleting a folder preserves its notes.

API
- /note-folders CRUD (GET, POST, PATCH, DELETE), all user-scoped.
- /notes POST/PATCH validate folder ownership before assignment (no cross-user
  folder bleed).
- Folder noteCount is tab-aware (active vs archived) via ?archived=.
- OpenAPI spec extended with /note-folders endpoints, NoteFolder schema, and
  folderId on SentNote/ReceivedNote. Codegen regenerated for api-client-react
  and api-zod (`pnpm --filter @workspace/api-spec run codegen`).

Client
- NoteFolder type and useNoteFolders / useCreateFolder / useUpdateFolder /
  useDeleteFolder / useMoveNoteToFolder hooks (optimistic across all
  ["notes", ...] caches; rollback on error).

UI (FoldersRail next to My Notes + Archive tabs only)
- Desktop: sidebar with All / Unfiled / user folders + counts.
- Mobile: horizontal chip row (flex + overflow-x-auto) above the notes grid.
- Per-folder kebab dropdown with Rename + Delete.
- Newly-created folder is auto-selected.
- HTML5 draggable note cards on desktop; touch long-press fallback (350ms)
  for iPad/mobile via shared drop pipeline (registerFolderDropHandler +
  hit-tested `[data-folder-drop]`).
- Dev-only `window.__notesTouchTest` helper (gated to non-production builds)
  exposes the touch pipeline so e2e tests can drive it deterministically
  without synthesizing native TouchEvents.

Bilingual
- notes.folders.* keys added to en.json and ar.json (RTL inherited from
  existing dir prop wired from i18n.language).

Tests (artifacts/tx-os/tests/notes-folders.spec.mjs)
- create folder + auto-select
- drag note → folder, refresh-and-still-in-folder persistence
- filter by folder / Unfiled / All
- drag between folders (count math)
- rename via kebab
- delete a non-empty folder via kebab → notes return to Unfiled (FK SET NULL)
- cross-user folder rejection (400)
- Arabic + RTL render
- separate touch test (414×800, hasTouch+isMobile) covers chip-row layout
  and exercises the touch drop pipeline through window helper.

All API node tests + tx-os Playwright suite + tsc clean.

artifacts/tx-os/src/pages/notes.tsx

@@ -137,6 +137,16 @@ export default function NotesPage() {
   const { data: folders = [] } = useNoteFolders(view === "archived");
   const moveNote = useMoveNoteToFolder();
   const showFolders = view === "active" || view === "archived";
+
+  // If the user switches tabs (or a folder is deleted) such that the current
+  // selection no longer exists in this view's folder set, fall back to "all"
+  // so they don't get stuck on an empty list.
+  useEffect(() => {
+    if (folderSelection.kind !== "folder") return;
+    if (!folders.some((f) => f.id === folderSelection.id)) {
+      setFolderSelection({ kind: "all" });
+    }
+  }, [folders, folderSelection]);
   const { data: receivedNotes = [], isLoading: loadingReceived } =
     useReceivedNotes(false);
   const { data: archivedReceivedNotes = [], isLoading: loadingArchivedReceived } =