M2 search: Postgres FTS backend + top search bar + results

- Migration 0005: generated tsvector column (title A + body B) + GIN index on
  notes; GET /api/notes/search?q= (websearch_to_tsquery, ts_rank, ACL-scoped,
  excludes trash), labels merged into results.
- Persistent AppShell layout (parent route + <RouterView> children) so the new
  top search box keeps focus across board/search/label navigation.
- SearchView (debounced live search from the shell → /search?q=, results masonry,
  no-match empty state); BoardView/SearchView render inside the shared shell.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

tests/test_notes.py

@@ -50,3 +50,9 @@ async def test_notes_create_requires_auth(app):
     client = app.test_client()
     resp = await client.post("/api/notes", json={"body": "hi"})
     assert resp.status_code == 401
+
+
+async def test_search_requires_auth(app):
+    client = app.test_client()
+    resp = await client.get("/api/notes/search?q=hello")
+    assert resp.status_code == 401