chore(models): finish the opus-5 replacement — no stale opus-4 fixtures remain

Every fixture, comment example, and panel mock that presented an Opus 4.x
id as current now carries claude-opus-5 (or the current sonnet/haiku ids in
the panel usage mocks). The only deliberate claude-opus-4 survivors are the
pricing-table fragment and its tests — they price the historical usage rows,
which would otherwise re-read as $0.

tests/integration/test_optimal_routes.py

@@ -940,7 +940,7 @@ async def test_review_code(optimal_client: AsyncClient) -> None:
 async def test_estimate_tokens(optimal_client: AsyncClient) -> None:
     response = await optimal_client.post(
         "/api/optimal/tokens/estimate",
-        json={"content": "Hello world", "model": "claude-opus-4-7"},
+        json={"content": "Hello world", "model": "claude-opus-5"},
         headers=_HDR,
     )
     assert response.status_code == HTTPStatus.OK