feat: Implement SQLite support with environment-driven backend switching

config/database.py

@@ -11,12 +11,21 @@ def _build_database_url() -> str:
     """Construct the SQLAlchemy database URL from granular environment vars.
 
     Falls back to `DATABASE_URL` for backward compatibility.
+    Supports SQLite when CALMINER_USE_SQLITE is set.
     """
 
     legacy_url = os.environ.get("DATABASE_URL", "")
     if legacy_url and legacy_url.strip() != "":
         return legacy_url
 
+    use_sqlite = os.environ.get("CALMINER_USE_SQLITE", "").lower() in ("true", "1", "yes")
+    if use_sqlite:
+        # Use SQLite database
+        db_path = os.environ.get("DATABASE_PATH", "./data/calminer.db")
+        # Ensure the directory exists
+        os.makedirs(os.path.dirname(db_path), exist_ok=True)
+        return f"sqlite:///{db_path}"
+
     driver = os.environ.get("DATABASE_DRIVER", "postgresql")
     host = os.environ.get("DATABASE_HOST")
     port = os.environ.get("DATABASE_PORT", "5432")