feat: upgrade MiniMax default to M2.7 + add new OpenRouter models

MiniMax: Add M2.7 and M2.7-highspeed as new defaults across provider
model lists, auxiliary client, metadata, setup wizard, RL training tool,
fallback tests, and docs. Retain M2.5/M2.1 as alternatives.

OpenRouter: Add grok-4.20-beta, nemotron-3-super-120b-a12b:free,
trinity-large-preview:free, glm-5-turbo, and hunter-alpha to the
model catalog.

MiniMax changes based on PR #1882 by @octo-patch (applied manually
due to stale conflicts in refactored pricing module).

tests/test_fallback_model.py

@@ -131,7 +131,7 @@ class TestTryActivateFallback:
 
     def test_activates_minimax_fallback(self):
         agent = _make_agent(
-            fallback_model={"provider": "minimax", "model": "MiniMax-M2.5"},
+            fallback_model={"provider": "minimax", "model": "MiniMax-M2.7"},
         )
         mock_client = _mock_resolve(
             api_key="sk-mm-key",
@@ -139,10 +139,10 @@ class TestTryActivateFallback:
         )
         with patch(
             "agent.auxiliary_client.resolve_provider_client",
-            return_value=(mock_client, "MiniMax-M2.5"),
+            return_value=(mock_client, "MiniMax-M2.7"),
         ):
             assert agent._try_activate_fallback() is True
-            assert agent.model == "MiniMax-M2.5"
+            assert agent.model == "MiniMax-M2.7"
             assert agent.provider == "minimax"
             assert agent.client is mock_client
 
@@ -165,7 +165,7 @@ class TestTryActivateFallback:
     def test_returns_false_when_no_api_key(self):
         """Fallback should fail gracefully when the API key env var is unset."""
         agent = _make_agent(
-            fallback_model={"provider": "minimax", "model": "MiniMax-M2.5"},
+            fallback_model={"provider": "minimax", "model": "MiniMax-M2.7"},
         )
         with patch(
             "agent.auxiliary_client.resolve_provider_client",