Fix SQLite database locking errors on HF Spaces

Fixes: sqlite3.OperationalError: database is locked

Changes:
- Increased connection timeout from 5s to 30s
- Enabled check_same_thread=False for multi-threading
- Added pool_pre_ping to verify connections
- Enabled SQLite WAL (Write-Ahead Logging) mode
- Set busy_timeout to 30 seconds
- Reduced synchronous mode to NORMAL for better performance

WAL mode allows concurrent reads while writing, preventing most
locking errors. Essential for HF Spaces with multiple workers.

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

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

app/__init__.py

@@ -29,8 +29,31 @@ def create_app():
 
     app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
 
+    # SQLite-specific settings to reduce locking issues
+    app.config['SQLALCHEMY_ENGINE_OPTIONS'] = {
+        'connect_args': {
+            'timeout': 30,  # Increase timeout to 30 seconds
+            'check_same_thread': False  # Allow multi-threaded access
+        },
+        'pool_pre_ping': True,  # Verify connections before using
+        'pool_recycle': 3600,  # Recycle connections every hour
+    }
+
     db.init_app(app)
 
+    # Enable WAL mode for SQLite to reduce locking
+    with app.app_context():
+        from sqlalchemy import event
+        from sqlalchemy.engine import Engine
+
+        @event.listens_for(Engine, "connect")
+        def set_sqlite_pragma(dbapi_conn, connection_record):
+            cursor = dbapi_conn.cursor()
+            cursor.execute("PRAGMA journal_mode=WAL")  # Write-Ahead Logging
+            cursor.execute("PRAGMA synchronous=NORMAL")  # Balance safety/performance
+            cursor.execute("PRAGMA busy_timeout=30000")  # 30 second timeout
+            cursor.close()
+
     # Import models
     from app.models import models