docs(api): add sync queue management documentation

- get_device_queue_stats.md - Get queue statistics for device
- list_device_queue_items.md - List queue items with filtering
- retry_queue_item.md - Retry failed queue items
- delete_queue_item.md - Delete queue items
- clear_device_queue.md - Clear entire device queue
- list_all_queue_items.md - List all queue items (admin)

Documents sync queue management for handling failed/queued operations
between devices and server

docs/developer/api/devices/approve_device_registration.md

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+# Approve Device Registration
+
+Approve a pending device registration request.
+
+**Endpoint**: `GET /api/devices/approve/:registration_id`
+**Auth**: Required (Admin only)
+
+## Path Parameters
+
+| Parameter | Type | Required | Description |
+|-----------|------|-----------|-------------|
+| registration_id | string (UUID) | Yes | Registration request UUID |
+
+## Request Headers
+
+| Header | Type | Required | Description |
+|--------|------|-----------|-------------|
+| Authorization | string | Yes | Bearer token (must have admin role) |
+
+### Example Request
+
+```http
+GET /api/devices/approve/550e8400-e29b-41d4-a716-446655440000
+Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
+```
+
+## Response (200 OK)
+
+```json
+{
+  "message": "Device registration approved",
+  "device_id": "uuid"
+}
+```
+
+## Error Responses
+
+| Code | Description |
+|------|-------------|
+| 401 | Invalid or expired token |
+| 403 | User does not have admin privileges |
+| 404 | Registration not found |
+| 400 | Registration already processed |
+
+## Try It Out
+
+<!-- API Explorer will be inserted here in Phase 3 -->

docs/developer/api/devices/delete_device.md

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+# Delete Device
+
+Delete a device and revoke its access.
+
+**Endpoint**: `DELETE /api/devices/:id`
+**Auth**: Required
+
+## Path Parameters
+
+| Parameter | Type | Required | Description |
+|-----------|------|-----------|-------------|
+| id | string (UUID) | Yes | Device UUID |
+
+## Request Headers
+
+| Header | Type | Required | Description |
+|--------|------|-----------|-------------|
+| Authorization | string | Yes | Bearer token |
+
+### Example Request
+
+```http
+DELETE /api/devices/550e8400-e29b-41d4-a716-446655440000
+Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
+```
+
+## Response (204 No Content)
+
+Device deleted successfully.
+
+## Error Responses
+
+| Code | Description |
+|------|-------------|
+| 401 | Invalid or expired token |
+| 403 | Device does not belong to user |
+| 404 | Device not found |
+
+## Try It Out
+
+<!-- API Explorer will be inserted here in Phase 3 -->

docs/developer/api/devices/list_pending_registrations.md

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+# List Pending Device Registrations
+
+List all pending device registration requests.
+
+**Endpoint**: `GET /api/devices/pending`
+**Auth**: Required (Admin only)
+
+## Request Headers
+
+| Header | Type | Required | Description |
+|--------|------|-----------|-------------|
+| Authorization | string | Yes | Bearer token (must have admin role) |
+
+### Example Request
+
+```http
+GET /api/devices/pending
+Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
+```
+
+## Response (200 OK)
+
+```json
+{
+  "registrations": [
+    {
+      "id": "uuid",
+      "device_name": "My Kobo",
+      "device_type": "kobo",
+      "user_email": "user@example.com",
+      "created_at": "2026-02-08T10:00:00Z"
+    }
+  ],
+  "total": 3
+}
+```
+
+## Error Responses
+
+| Code | Description |
+|------|-------------|
+| 401 | Invalid or expired token |
+| 403 | User does not have admin privileges |
+
+## Try It Out
+
+<!-- API Explorer will be inserted here in Phase 3 -->

docs/developer/api/devices/reject_device_registration.md

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+# Reject Device Registration
+
+Reject a pending device registration request.
+
+**Endpoint**: `POST /api/devices/reject/:registration_id`
+**Auth**: Required (Admin only)
+
+## Path Parameters
+
+| Parameter | Type | Required | Description |
+|-----------|------|-----------|-------------|
+| registration_id | string (UUID) | Yes | Registration request UUID |
+
+## Request Headers
+
+| Header | Type | Required | Description |
+|--------|------|-----------|-------------|
+| Authorization | string | Yes | Bearer token (must have admin role) |
+
+### Example Request
+
+```http
+POST /api/devices/reject/550e8400-e29b-41d4-a716-446655440000
+Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
+```
+
+## Response (200 OK)
+
+```json
+{
+  "message": "Device registration rejected"
+}
+```
+
+## Error Responses
+
+| Code | Description |
+|------|-------------|
+| 401 | Invalid or expired token |
+| 403 | User does not have admin privileges |
+| 404 | Registration not found |
+| 400 | Registration already processed |
+
+## Try It Out
+
+<!-- API Explorer will be inserted here in Phase 3 -->

docs/developer/api/devices/update_device.md

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+# Update Device
+
+Update a device's information.
+
+**Endpoint**: `PUT /api/devices/:id`
+**Auth**: Required
+**Content-Type**: `application/json`
+
+## Path Parameters
+
+| Parameter | Type | Required | Description |
+|-----------|------|-----------|-------------|
+| id | string (UUID) | Yes | Device UUID |
+
+## Request Body
+
+| Field | Type | Required | Description |
+|--------|------|-----------|-------------|
+| name | string | No | Device display name |
+| device_type | string | No | Device type (kobo, koreader, etc.) |
+
+### Example Request
+
+```json
+{
+  "name": "My Kobo Clara",
+  "device_type": "kobo"
+}
+```
+
+## Response (200 OK)
+
+```json
+{
+  "id": "uuid",
+  "name": "My Kobo Clara",
+  "device_type": "kobo",
+  "user_id": "user-uuid",
+  "status": "active",
+  "created_at": "2026-02-08T10:00:00Z",
+  "updated_at": "2026-02-08T11:00:00Z"
+}
+```
+
+## Error Responses
+
+| Code | Description |
+|------|-------------|
+| 400 | Invalid request data |
+| 401 | Invalid or expired token |
+| 403 | Device does not belong to user |
+| 404 | Device not found |
+
+## Try It Out
+
+<!-- API Explorer will be inserted here in Phase 3 -->