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 -->

docs/api/notes/delete_note.md

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+# Delete Note
+
+Delete a note.
+
+**Endpoint**: `DELETE /api/media-items/notes/{note_id}`
+**Auth**: Required
+
+## Path Parameters
+
+| Parameter | Type | Required | Description |
+|-----------|------|-----------|-------------|
+| note_id | string | Yes | Note UUID |
+
+## Request Headers
+
+| Header | Type | Required | Description |
+|--------|------|-----------|-------------|
+| Authorization | string | Yes | Bearer token |
+
+### Example Request
+
+```http
+DELETE /api/media-items/notes/uuid
+Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
+```
+
+## Response (204 No Content)
+
+Note deleted successfully.
+
+## Error Responses
+
+| Code | Description |
+|------|-------------|
+| 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 -->

docs/api/notes/get_notes.md

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+# Get Notes
+
+Retrieve all notes for a specific media item.
+
+**Endpoint**: `GET /api/media-items/{media_id}/notes`
+**Auth**: Required
+
+## Path Parameters
+
+| Parameter | Type | Required | Description |
+|-----------|------|-----------|-------------|
+| media_id | string | Yes | Media item UUID |
+
+## Request Headers
+
+| Header | Type | Required | Description |
+|--------|------|-----------|-------------|
+| Authorization | string | Yes | Bearer token |
+
+### Example Request
+
+```http
+GET /api/media-items/uuid/notes
+Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
+```
+
+## Response (200 OK)
+
+```json
+{
+  "notes": [
+    {
+      "id": "uuid",
+      "media_item_id": "uuid",
+      "user_id": "uuid",
+      "content": "This is an interesting passage...",
+      "position": "epubcfi(/6/4/2:15)",
+      "percentage_location": 0.45,
+      "character_start": 15432,
+      "character_end": 15480,
+      "epubcfi_location": "epubcfi(/6/4/2:15)",
+      "created_at": "2026-01-31T10:00:00Z",
+      "updated_at": "2026-01-31T10:00:00Z"
+    }
+  ]
+}
+```
+
+## Error Responses
+
+| Code | Description |
+|------|-------------|
+| 401 | Invalid or expired token |
+| 404 | Media item not found |
+
+## Try It Out
+
+<!-- API Explorer will be inserted here in Phase 3 -->

docs/api/notes/update_note.md

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+# 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 -->