feat: SAC 0.7.4 sidebar system stats block with UI toggle

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/tests/test_system_stats.py

@@ -0,0 +1,30 @@
+"""GET /api/v1/system/stats"""
+
+from app.services.ui_settings import upsert_ui_settings
+
+
+def test_system_stats_requires_auth(client):
+    response = client.get("/api/v1/system/stats")
+    assert response.status_code == 401
+
+
+def test_system_stats_visible_default(jwt_headers, client):
+    response = client.get("/api/v1/system/stats", headers=jwt_headers)
+    assert response.status_code == 200
+    body = response.json()
+    assert body["visible"] is True
+    assert "collected_at" in body
+    assert "database" in body
+    assert body["database"]["status"] in ("ok", "error")
+    assert "app" in body
+    assert "events_last_hour" in body["app"]
+    assert "problems_open" in body["app"]
+
+
+def test_system_stats_respects_ui_setting(jwt_headers, client, db_session):
+    upsert_ui_settings(db_session, show_sidebar_system_stats=False)
+    db_session.commit()
+
+    response = client.get("/api/v1/system/stats", headers=jwt_headers)
+    assert response.status_code == 200
+    assert response.json()["visible"] is False