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/users/get_profile.md

@@ -2,7 +2,7 @@
 
 Retrieve the current authenticated user's profile.
 
-**Endpoint**: `GET /api/users/me`
+**Endpoint**: `GET /api/auth/profile`
 **Auth**: Required
 
 ## Request Headers
@@ -14,7 +14,7 @@ Retrieve the current authenticated user's profile.
 ### Example Request
 
 ```http
-GET /api/users/me
+GET /api/auth/profile
 Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
 ```