refactor: migrate database to SQLModel and implement modular DB structure

decnet/web/db/sqlite/database.py

@@ -0,0 +1,30 @@
+from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession, async_sessionmaker
+from sqlalchemy import create_engine
+from sqlmodel import SQLModel
+from pathlib import Path
+
+# We need both sync and async engines for SQLite
+# Sync for initialization (DDL) and async for standard queries
+
+def get_async_engine(db_path: str):
+    # aiosqlite driver for async access
+    return create_async_engine(f"sqlite+aiosqlite:///{db_path}", echo=False, connect_args={"uri": True})
+
+def get_sync_engine(db_path: str):
+    return create_engine(f"sqlite:///{db_path}", echo=False, connect_args={"uri": True})
+
+def init_db(db_path: str):
+    """Synchronously create all tables."""
+    engine = get_sync_engine(db_path)
+    # Ensure WAL mode is set
+    with engine.connect() as conn:
+        conn.exec_driver_sql("PRAGMA journal_mode=WAL")
+        conn.exec_driver_sql("PRAGMA synchronous=NORMAL")
+    SQLModel.metadata.create_all(engine)
+
+async def get_session(engine) -> AsyncSession:
+    async_session = async_sessionmaker(
+        engine, class_=AsyncSession, expire_on_commit=False
+    )
+    async with async_session() as session:
+        yield session