feat(admin): add admin_actions audit table and log/list functions

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/admin/db.py

@@ -0,0 +1,26 @@
+import sqlite3
+from datetime import datetime, timezone
+
+from src.auth.db import get_conn
+
+
+def _now() -> str:
+    return datetime.now(timezone.utc).isoformat()
+
+
+def log_action(
+    admin_email: str, action: str, target_user_id: int | None, details: str | None
+) -> None:
+    get_conn().execute(
+        "INSERT INTO admin_actions (admin_email, action, target_user_id, details, created_at) "
+        "VALUES (?, ?, ?, ?, ?)",
+        (admin_email, action, target_user_id, details, _now()),
+    )
+
+
+def list_actions(limit: int = 200) -> list[sqlite3.Row]:
+    return (
+        get_conn()
+        .execute("SELECT * FROM admin_actions ORDER BY id DESC LIMIT ?", (limit,))
+        .fetchall()
+    )