docs: add progress, notes, and highlights API endpoints

Phase 2 part 4: Split reading progress and annotation endpoints
- Progress: get_progress, update_progress, delete_progress
- Notes: get_notes, create_note, update_note, delete_note
- Highlights: get_highlights, create_highlight, update_highlight, delete_highlight
- All endpoints support EPUB CFI and percentage locations

docs/api/notes/update_note.md

@@ -0,0 +1,55 @@
+# Update Note
+
+Update an existing note.
+
+**Endpoint**: `PUT /api/media-items/notes/{note_id}`
+**Auth**: Required
+**Content-Type**: `application/json`
+
+## Path Parameters
+
+| Parameter | Type | Required | Description |
+|-----------|------|-----------|-------------|
+| note_id | string | Yes | Note UUID |
+
+## Request Body
+
+| Field | Type | Required | Description |
+|--------|------|-----------|-------------|
+| content | string | No | Updated note content |
+| position | string | No | Updated location reference |
+
+### Example Request
+
+```json
+{
+  "content": "Updated note content",
+  "position": "epubcfi(/6/4/2:20)"
+}
+```
+
+## Response (200 OK)
+
+```json
+{
+  "id": "uuid",
+  "media_item_id": "uuid",
+  "user_id": "uuid",
+  "content": "Updated note content",
+  "position": "epubcfi(/6/4/2:20)",
+  "updated_at": "2026-01-31T10:00:00Z"
+}
+```
+
+## Error Responses
+
+| Code | Description |
+|------|-------------|
+| 400 | Invalid note data |
+| 401 | Invalid or expired token |
+| 403 | User does not own this note |
+| 404 | Note not found |
+
+## Try It Out
+
+<!-- API Explorer will be inserted here in Phase 3 -->