Add admin user seeding functionality and corresponding tests

backend/app/db.py

@@ -75,3 +75,26 @@ def _run_migrations(conn: duckdb.DuckDBPyConnection) -> None:
             created_at   TIMESTAMP DEFAULT now()
         )
     """)
+    _seed_admin(conn)
+
+
+def _seed_admin(conn: duckdb.DuckDBPyConnection) -> None:
+    """Insert the default admin user if it doesn't already exist."""
+    from passlib.context import CryptContext
+    _pwd = CryptContext(schemes=["bcrypt"], deprecated="auto")
+
+    email = os.getenv("ADMIN_EMAIL", "ai@allucanget.biz")
+    password = os.getenv("ADMIN_PASSWORD", "admin123")
+
+    existing = conn.execute(
+        "SELECT id FROM users WHERE email = ?", [email]
+    ).fetchone()
+    if existing is None:
+        password_hash = _pwd.hash(password)
+        conn.execute(
+            """
+            INSERT INTO users (email, password_hash, role)
+            VALUES (?, ?, 'admin')
+            """,
+            [email, password_hash],
+        )