New frontmatter'd docs with real shapes (sqlc models pinned directly):
- bookmarks: get/create/update/delete (sync-aware rows: dedup_key,
last_modified_*, tombstones; delete is 204)
- review: upsert (empty string DELETES the review) / get (200 with
{review:null} when absent) / delete
- get single note + highlight (full sqlc row shapes)
- annotation history: restore (POST, kind via query or body) and purge
(DELETE, kind via required query; permanent)
Gate hardening forced by this batch:
- required-field walk now guards non-struct Request types (RawMessage pins)
- update_media_bookmark needed a full example block (no cross-reference
shortcuts — the gate checks every doc standalone)
