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/create_note.md

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+# Create Note
+
+Create a new note for a media item.
+
+**Endpoint**: `POST /api/media-items/{media_id}/notes`
+**Auth**: Required
+**Content-Type**: `application/json`
+
+## Path Parameters
+
+| Parameter | Type | Required | Description |
+|-----------|------|-----------|-------------|
+| media_id | string | Yes | Media item UUID |
+
+## Request Body
+
+| Field | Type | Required | Description |
+|--------|------|-----------|-------------|
+| content | string | Yes | Note content |
+| position | string | No | Location reference (e.g., epubcfi) |
+| percentage_location | float | No | Location as percentage (0-1) |
+| epubcfi_location | string | No | EPUB CFI location |
+
+### Example Request
+
+```json
+{
+  "content": "This is a note",
+  "position": "epubcfi(/6/4/2:15)",
+  "percentage_location": 0.45,
+  "epubcfi_location": "epubcfi(/6/4/2:15)"
+}
+```
+
+## Response (201 Created)
+
+```json
+{
+  "id": "uuid",
+  "media_item_id": "uuid",
+  "user_id": "uuid",
+  "content": "This is a note",
+  "position": "epubcfi(/6/4/2:15)",
+  "percentage_location": 0.45,
+  "epubcfi_location": "epubcfi(/6/4/2:15)",
+  "created_at": "2026-01-31T10:00:00Z"
+}
+```
+
+## Error Responses
+
+| Code | Description |
+|------|-------------|
+| 400 | Invalid note data |
+| 401 | Invalid or expired token |
+| 404 | Media item not found |
+
+## Try It Out
+
+<!-- API Explorer will be inserted here in Phase 3 -->