M3 wiki-links: [[links]] + backlinks

- Migration 0009: note_links (source_id, target_norm). Parse [[...]] from body on
  create/update and rewrite the source's links. GET /api/notes/titles (owner
  {id,title} index for client-side resolution); GET /api/notes/<id>/backlinks.
- Frontend: titles store; LinkedText renders [[Title]] styled on cards; editor
  shows Links (outgoing, resolve/create-on-click) + Linked-from (backlinks),
  clicking navigates the editor to the target note (board + search).
- notes store: fetchOne, createTitled. DB-free link-parser tests.

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

tests/test_notes.py

@@ -2,7 +2,7 @@ import pytest
 
 from thoughtsync.app import create_app
 from thoughtsync.models.note import NOTE_COLORS, Note
-from thoughtsync.notes import is_empty_note, normalize_color
+from thoughtsync.notes import is_empty_note, normalize_color, parse_link_titles
 
 
 @pytest.fixture
@@ -74,3 +74,19 @@ async def test_reorder_requires_auth(app):
     client = app.test_client()
     resp = await client.post("/api/notes/reorder", json={"ids": []})
     assert resp.status_code == 401
+
+
+def test_parse_link_titles():
+    titles = parse_link_titles("see [[Alpha]] and [[ beta ]] and [[Alpha]] again")
+    assert titles == ["alpha", "beta"]
+
+
+def test_parse_link_titles_empty():
+    assert parse_link_titles(None) == []
+    assert parse_link_titles("no links here") == []
+
+
+async def test_titles_requires_auth(app):
+    client = app.test_client()
+    resp = await client.get("/api/notes/titles")
+    assert resp.status_code == 401