feat: Add Chat UX improvements with notifications and @mention support

- Add ActionBar component with expandable toolbar for mobile
- Add @mention functionality with autocomplete dropdown
- Add browser notification system (push, sound, vibration)
- Add NotificationSettings modal for user preferences
- Add mention badges on room list cards
- Add ReportPreview with Markdown rendering and copy/download
- Add message copy functionality with hover actions
- Add backend mentions field to messages with Alembic migration
- Add lots field to rooms, remove templates
- Optimize WebSocket database session handling
- Various UX polish (animations, accessibility)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/core/database.py

@@ -3,20 +3,23 @@
 Supports MySQL database with connection pooling.
 All tables use 'tr_' prefix to avoid conflicts in shared database.
 """
+from contextlib import contextmanager
 from sqlalchemy import create_engine
 from sqlalchemy.ext.declarative import declarative_base
-from sqlalchemy.orm import sessionmaker
+from sqlalchemy.orm import sessionmaker, Session
 from app.core.config import get_settings
 
 settings = get_settings()
 
 # Create engine with MySQL connection pooling
+# Pool settings are configurable via environment variables
 engine = create_engine(
     settings.DATABASE_URL,
-    pool_size=5,
-    max_overflow=10,
+    pool_size=settings.DB_POOL_SIZE,
+    max_overflow=settings.DB_MAX_OVERFLOW,
+    pool_timeout=settings.DB_POOL_TIMEOUT,
     pool_pre_ping=True,  # Verify connection before using
-    pool_recycle=3600,  # Recycle connections after 1 hour
+    pool_recycle=settings.DB_POOL_RECYCLE,
     echo=settings.DEBUG,
 )
 
@@ -34,3 +37,21 @@ def get_db():
         yield db
     finally:
         db.close()
+
+
+@contextmanager
+def get_db_context() -> Session:
+    """Context manager for short-lived database sessions.
+
+    Use this for operations that need a database session but should
+    not hold onto it for the entire request/connection lifecycle.
+
+    Example:
+        with get_db_context() as db:
+            result = db.query(Model).filter(...).first()
+    """
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()