- Label + NoteLabel models; migration 0004 (labels unique per owner + note_labels join, cascade). - /api/labels: list/create(idempotent)/rename(clash-checked)/delete, owner-scoped. - PUT /api/notes/<id>/labels to set a note's labels (validated against owned). - Note responses now include labels[] (merged via one explicit join query — no lazy relationship); GET /api/notes?...&label=<id> filters by label. - DB-free auth-guard tests for labels endpoints. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm