fix(insta-lab): 선별 zero-pref 크래시 가드 + judge max_tokens 상향 + 404 테스트

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

insta-lab/tests/test_ranked_decision_api.py

@@ -40,3 +40,8 @@ def test_decision_invalid_400(client):
     sid = db.add_card_slate({"keyword": "x", "category": "economy"})
     r = client.post(f"/api/insta/slates/{sid}/decision", json={"decision": "maybe"})
     assert r.status_code == 400
+
+
+def test_decision_unknown_slate_404(client):
+    r = client.post("/api/insta/slates/99999/decision", json={"decision": "approved"})
+    assert r.status_code == 404