Add password visibility toggle to login; auto-sync admin password from ENV

- Login.tsx: Eye/EyeOff toggle button on password field
- main.py: _seed_admin() now updates stored bcrypt hash when ENV password changed

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

backend/app/main.py

@@ -10,7 +10,7 @@ from apscheduler.schedulers.asyncio import AsyncIOScheduler
 from .database import init_db, AsyncSessionLocal
 from .config import get_settings
 from .models import User, Library
-from .services.auth import hash_password, create_token
+from .services.auth import hash_password, verify_password, create_token
 from .services.file_watcher import start_file_watcher, stop_file_watcher
 from .services.podcast_feed import update_all_feeds
 from sqlalchemy import select
@@ -25,7 +25,12 @@ async def _seed_admin():
     settings = get_settings()
     async with AsyncSessionLocal() as db:
         result = await db.execute(select(User).where(User.is_admin == True))
-        if result.scalar_one_or_none():
+        existing = result.scalar_one_or_none()
+        if existing:
+            if not verify_password(settings.admin_password, existing.password_hash):
+                existing.password_hash = hash_password(settings.admin_password)
+                await db.commit()
+                logger.info("Admin-Passwort aus ENV aktualisiert.")
             return
         logger.info(f"Lege Admin-User an: {settings.admin_username}")
         admin = User(