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/analytics/get_analytics.md

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+# Get Reading Statistics
+
+Retrieve reading statistics for a date range.
+
+**Endpoint**: `GET /api/analytics/reading-stats`
+**Auth**: Required
+
+## Query Parameters
+
+| Parameter | Type | Required | Description |
+|-----------|------|-----------|-------------|
+| start_date | string | No | Start date (ISO 8601 format) |
+| end_date | string | No | End date (ISO 8601 format) |
+
+## Request Headers
+
+| Header | Type | Required | Description |
+|--------|------|-----------|-------------|
+| Authorization | string | Yes | Bearer token |
+
+### Example Request
+
+```http
+GET /api/analytics/reading-stats?start_date=2026-01-01&end_date=2026-01-31
+Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
+```
+
+## Response (200 OK)
+
+```json
+{
+  "pages_read": 1250,
+  "books_completed": 5,
+  "reading_time_hours": 42.5,
+  "sessions_count": 28,
+  "average_session_minutes": 91
+}
+```
+
+## Error Responses
+
+| Code | Description |
+|------|-------------|
+| 400 | Invalid date format |
+| 401 | Invalid or expired token |
+
+## Try It Out
+
+<!-- API Explorer will be inserted here in Phase 3 -->