M1: notes model + migration 0002 + notes API (CRUD, trash/restore)

- Note model (owner_id, title, body, color-key, pinned, archived, deleted_at
  soft-delete, timestamps) + board index; NOTE_COLORS palette keys.
- Migration 0002 (notes table + ix_notes_owner_board).
- /api/notes blueprint (login_required): list (?filter=active|archived|trash,
  pinned-then-updated, read via visible_to_user ACL), create, get, patch
  (title/body/color/pinned/archived), trash, restore, permanent delete
  (trash-only). Mutations owner-scoped; empty note rejected (400).
- DB-free unit tests: is_empty_note, normalize_color, palette, serialize,
  auth-guard on list/create.

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, share, user  # noqa: F401
+from . import group, note, share, user  # noqa: F401