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

src/thoughtsync/models/all.py

@@ -3,4 +3,4 @@
 Imported for side effects only (model registration on Base.metadata).
 """
 
-from . import group, label, note, note_attachment, note_item, settings, share, user  # noqa: F401
+from . import group, label, note, note_attachment, note_item, note_link, settings, share, user  # noqa: F401

src/thoughtsync/models/note_link.py

@@ -0,0 +1,23 @@
+from __future__ import annotations
+
+import uuid
+
+from sqlalchemy import ForeignKey, Index, Text
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column
+
+from . import Base
+
+
+class NoteLink(Base):
+    """A [[wiki-link]] from a source note to a target title (normalized). Resolved
+    to a target note by matching target_norm against lower(trim(note.title))."""
+
+    __tablename__ = "note_links"
+    __table_args__ = (Index("ix_note_links_target", "target_norm"),)
+
+    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    source_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("notes.id", ondelete="CASCADE"), nullable=False
+    )
+    target_norm: Mapped[str] = mapped_column(Text(), nullable=False)