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/create_media_bookmark.md

@@ -0,0 +1,76 @@
+---
+method: POST
+path: /api/media-items/:id/bookmarks
+auth: jwt
+area: media-items
+---
+<!-- source: internal/handlers/media.go:2206 MediaHandler.CreateMediaBookmark -->
+
+# Create Media Bookmark
+
+Creates a bookmark through the sync-aware path (dedup + last-write-wins +
+tombstones). Returns **201** with the stored bookmark row.
+
+## Example request
+
+```json example-request
+{
+  "title": "Chapter 3",
+  "position": "kindle:pos:1:2",
+  "notes": "revisit this",
+  "cfi_position": "epubcfi(/6/4)",
+  "page_number": 42,
+  "chapter_number": 3,
+  "percentage": 35.5,
+  "chapter_reference": 3,
+  "origin": "android"
+}
+```
+
+## 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": 42,
+  "chapter_number": 3,
+  "cfi_position": "epubcfi(/6/4)",
+  "title": "Chapter 3",
+  "position": "kindle:pos:1:2",
+  "notes": "revisit this",
+  "created_at": "2026-10-24T13:57:01Z",
+  "dedup_key": "kindle:pos:1:2",
+  "last_modified_at": "2026-10-24T13:57:01Z",
+  "last_modified_source": "android",
+  "device_sync_data": null,
+  "percentage_location": 35.5,
+  "epubcfi_location": "epubcfi(/6/4)",
+  "chapter_reference": 3,
+  "deleted": false,
+  "deleted_at": null,
+  "origin_source": "android"
+}
+```
+
+## Request fields
+
+| Field | Type | Required | Notes |
+| ----- | ---- | -------- | ----- |
+| title | string | yes | 1–255 chars |
+| position | string | no | ≤100 chars |
+| notes | string | no | ≤100000 chars |
+| cfi_position | string | no | ≤255 chars |
+| page_number | number | no | |
+| chapter_number | number | no | |
+| percentage | number | no | |
+| chapter_reference | number | no | |
+| origin | string | no | client label ("android", "web"); defaults to "web" |
+
+## Errors
+
+| Status | Body | When |
+| ------ | ---- | ---- |
+| 400 | `{"error": "invalid request"}` / validation error | malformed body |
+| 500 | `{"error": "..."}` | annotation service failure |