docs(api): complete backend documentation with all missing endpoints

Complete API documentation audit covering all backend endpoints.

Auth Endpoints:
- Fixed endpoint paths from /api/users/me/* to /api/auth/*
- Added update_email.md and update_username.md

Device Management:
- Device shelf operations (add, get, remove, clear)
- Device CRUD operations (update, delete)
- Registration management (pending, approve, reject)

Books Operations:
- Bulk delete and bulk update with normalization
- Download endpoint with format-specific headers

Conflict Resolution:
- Complete conflict management (list, get, resolve, delete)
- Bulk operations (bulk resolve, bulk dismiss, dismiss all)

Sync Protocols:
- KOReader: progress, metadata, library, bookmarks
- Kobo: markup, bookmarks, analytics, initialization, server sync

Scanner:
- Enhanced docs with manga/comic support
- Added 148-line comprehensive overview
- All formats documented (ebooks, comics, manga)

WebSocket:
- Comprehensive real-time sync API
- Messages, topics, authentication, examples

Documentation:
- Updated api-reference.md with all 122+ endpoints
- Updated index.md with new categories

Total: 36 new files, 6 modified files, 100% coverage

docs/developer/api/scanner/get_scan_status.md

@@ -0,0 +1,73 @@
+# Get Scan Status
+
+Get the status of a specific scan job.
+
+**Endpoint**: `GET /api/scanner/status/:jobId`
+**Auth**: Required (Admin only)
+
+## Path Parameters
+
+| Parameter | Type | Required | Description |
+|-----------|------|-----------|-------------|
+| jobId | string (UUID) | Yes | Scan job UUID |
+
+## Request Headers
+
+| Header | Type | Required | Description |
+|--------|------|-----------|-------------|
+| Authorization | string | Yes | Bearer token (must have admin role) |
+
+### Example Request
+
+```http
+GET /api/scanner/status/550e8400-e29b-41d4-a716-446655440000
+Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
+```
+
+## Response (200 OK)
+
+```json
+{
+  "job_id": "uuid",
+  "library_id": "uuid",
+  "status": "in_progress",
+  "started_at": "2026-02-08T10:00:00Z",
+  "updated_at": "2026-02-08T10:05:00Z",
+  "progress": {
+    "total_files": 1523,
+    "scanned_files": 850,
+    "added_files": 125,
+    "updated_files": 45,
+    "failed_files": 3,
+    "percentage": 55.8
+  },
+  "errors": [
+    {
+      "file_path": "/path/to/file.epub",
+      "error": "Invalid EPUB format"
+    }
+  ]
+}
+```
+
+## Status Values
+
+| Status | Description |
+|--------|-------------|
+| pending | Job is queued |
+| in_progress | Job is currently running |
+| completed | Job completed successfully |
+| failed | Job failed with errors |
+| cancelled | Job was cancelled |
+
+## Error Responses
+
+| Code | Description |
+|------|-------------|
+| 401 | Invalid or expired token |
+| 403 | User does not have admin privileges |
+| 404 | Job not found |
+
+## Try It Out
+
+<!-- API Explorer will be inserted here in Phase 3 -->