docs: add ratings, devices, and analytics API endpoints

Phase 2 part 5: Split device management and analytics endpoints
- Ratings: get_ratings, create_rating (1-10 scale with half-stars)
- Devices: register_device, list_devices, get_devices, revoke_device
- Analytics: get_analytics (reading statistics)
- Include device registration flow details

docs/api/ratings/create_rating.md

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+# Create Rating
+
+Set a rating for a media item. Creates a new rating or updates an existing one.
+
+**Endpoint**: `POST /api/media-items/{media_id}/rating`
+**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 |
+|--------|------|-----------|-------------|
+| rating | integer | Yes | Rating from 1-10 |
+
+### Example Request
+
+```json
+{
+  "rating": 8
+}
+```
+
+## Response (201 Created)
+
+```json
+{
+  "rating": 8,
+  "user_id": "uuid",
+  "media_item_id": "uuid",
+  "created_at": "2026-01-31T10:00:00Z"
+}
+```
+
+**Rating Scale**: 1-10 (odd numbers = half-stars: 1=0.5★, 2=1★, 3=1.5★, ..., 9=4.5★, 10=5★)
+
+## Error Responses
+
+| Code | Description |
+|------|-------------|
+| 400 | Invalid rating (must be 1-10) |
+| 401 | Invalid or expired token |
+| 404 | Media item not found |
+
+## Try It Out
+
+<!-- API Explorer will be inserted here in Phase 3 -->