Case-insensitive login, auto-matching after scan, per-library sources

- auth: username lookup is now case-insensitive via func.lower()
- scanner: trigger match_audiobook for each newly found item after scan
- matcher: read match_sources from library settings; refactored to loop
  over configured sources in priority order instead of hardcoded sequence
- schemas/routers: expose matchSources in LibraryOut API response
- Admin UI: pill-toggle for MusicBrainz/Open Library/Google Books per library

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/services/scanner.py

@@ -1,5 +1,6 @@
 import os
 import uuid
+import asyncio
 import logging
 from datetime import datetime
 from pathlib import Path
@@ -110,6 +111,7 @@ async def scan_library_task(library_id: str, job_id: str):
                     all_books.extend(_discover_audiobook_folders(folder_path))
 
             items_found = 0
+            new_item_ids: list[str] = []
             for book_info in all_books:
                 folder_path = book_info["path"]
                 audio_files = book_info["files"]
@@ -164,6 +166,8 @@ async def scan_library_task(library_id: str, job_id: str):
                         )
                         db.add(bf)
 
+                    new_item_ids.append(item.id)
+
                 items_found += 1
 
             await db.commit()
@@ -187,6 +191,12 @@ async def scan_library_task(library_id: str, job_id: str):
 
             logger.info(f"Scan abgeschlossen: {items_found} Items in Library {library_id}")
 
+            # Auto-Matching für neue Items starten
+            if new_item_ids:
+                from .matcher import match_audiobook
+                for iid in new_item_ids:
+                    asyncio.create_task(match_audiobook(iid))
+
         except Exception as e:
             logger.error(f"Scan-Fehler für Library {library_id}: {e}", exc_info=True)
             async with AsyncSessionLocal() as err_db: