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/unit/services/test_usage.py

@@ -629,7 +629,7 @@ class TestGetByModel:
                 cost_usd=0.02,
             ),
             _make_row(
-                model="claude-opus-4-5",
+                model="claude-opus-5",
                 tokens_input=100,
                 tokens_output=100,
                 tokens_cache_read=0,