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/list_pending_registrations.md

@@ -0,0 +1,47 @@
+# 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 -->