docs(api): add new endpoint documentation

- Add create_media_item.md for media item creation API

- Add delete_rating.md for rating deletion endpoint

- Add update_rating.md for rating update endpoint

docs/developer/api/ratings/delete_rating.md

@@ -0,0 +1,38 @@
+# Delete Rating
+
+Delete the current user's rating for a media item.
+
+**Endpoint**: `DELETE /api/media-items/{media_id}/rating`
+**Auth**: Required
+
+## Path Parameters
+
+| Parameter | Type | Required | Description |
+|-----------|------|-----------|-------------|
+| media_id | string | Yes | Media item UUID |
+
+### Example Request
+
+```http
+DELETE /api/media-items/550e8400-e29b-41d4-a716-446655440000/rating
+Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
+```
+
+## Response (200 OK)
+
+```json
+{
+  "message": "Rating deleted successfully"
+}
+```
+
+## Error Responses
+
+| Code | Description |
+|------|-------------|
+| 401 | Invalid or expired token |
+| 404 | Media item or rating not found |
+
+## Try It Out
+
+<!-- API Explorer will be inserted here in Phase 3 -->