docs(media-items): Work Order 3 batch 3a — reader-adjacent CRUD (11 endpoints)

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)

docs/developer/api/media-items/get_media_bookmarks.md

@@ -0,0 +1,51 @@
+---
+method: GET
+path: /api/media-items/:id/bookmarks
+auth: jwt
+area: media-items
+---
+<!-- source: internal/handlers/media.go:2181 MediaHandler.GetMediaBookmarks -->
+
+# Get Media Bookmarks
+
+Lists the signed-in user's bookmarks for one media item (sync-aware rows:
+dedup key and last-writer bookkeeping included).
+
+## Example response
+
+```json example-response
+[
+  {
+    "id": "110e8400-e29b-41d4-a716-446655440000",
+    "media_item_id": "550e8400-e29b-41d4-a716-446655440000",
+    "user_id": "92413c3a-e1b8-4fff-b3f9-95c74478d19a",
+    "page_number": null,
+    "chapter_number": null,
+    "cfi_position": null,
+    "title": "Chapter 3",
+    "position": "kindle:pos:1:2",
+    "notes": null,
+    "created_at": "2026-10-24T13:57:01Z",
+    "dedup_key": "kindle:pos:1:2",
+    "last_modified_at": "2026-10-24T13:57:01Z",
+    "last_modified_source": "web",
+    "device_sync_data": null,
+    "percentage_location": null,
+    "epubcfi_location": null,
+    "chapter_reference": null,
+    "deleted": false,
+    "deleted_at": null,
+    "origin_source": "web"
+  }
+]
+```
+
+`device_sync_data` is `[]byte` → base64 string when set, `null` otherwise.
+pgtype fields are `null` when unset.
+
+## Errors
+
+| Status | Body | When |
+| ------ | ---- | ---- |
+| 400 | `{"error": "invalid user"}` / `{"error": "invalid media item id"}` | malformed ids |
+| 500 | `{"error": "..."}` | unexpected server error |