chore(models): move the opus alias to claude-opus-5

Claude Opus 5 released today — same $5/$25 sticker, 1M context; Opus 4.8
moves to legacy. The pricing table gains a dedicated claude-opus-5
fragment (the claude-opus-4 substring doesn't cover it, so without the
row the fleet's Opus usage would silently cost-track as $0 — exactly
what test_opus_is_priced now guards).

tests/unit/models/test_misc_models.py

@@ -106,7 +106,7 @@ def test_build_anthropic_entries_skips_missing_models() -> None:
     # Patch MODEL_MAP to be missing one entry → loop hits the `continue` branch.
     with patch(
         "roboco.models.llm_catalog.MODEL_MAP",
-        {"opus": "claude-opus-4-8"},  # sonnet+haiku missing
+        {"opus": "claude-opus-5"},  # sonnet+haiku missing
     ):
         entries = _build_anthropic_entries()
     # Only one entry survives — opus.

tests/unit/models/test_model_map.py

@@ -12,10 +12,9 @@ def test_sonnet_alias_resolves_to_sonnet_5() -> None:
     assert MODEL_MAP["sonnet"] == "claude-sonnet-5"
 
 
-def test_opus_alias_resolves_to_opus_4_8() -> None:
-    # CEO upgrade to the newest Opus tier ("Opus 5" does not exist — the
-    # Claude 5 family is Fable/Mythos/Sonnet; Opus tops out at 4.8).
-    assert MODEL_MAP["opus"] == "claude-opus-4-8"
+def test_opus_alias_resolves_to_opus_5() -> None:
+    # CEO upgrade to the newest Opus tier (Opus 5, released 2026-07-25).
+    assert MODEL_MAP["opus"] == "claude-opus-5"
 
 
 def test_sonnet_5_is_priced() -> None: