Fix #5211: Preserve dots in OpenCode Go model names

OpenCode Go model names with dots (minimax-m2.7, glm-4.5, kimi-k2.5)
were being mangled to hyphens (minimax-m2-7), causing HTTP 401 errors.

Two code paths were affected:
1. model_normalize.py: opencode-go was incorrectly in DOT_TO_HYPHEN_PROVIDERS
2. run_agent.py: _anthropic_preserve_dots() did not check for opencode-go

Fix:
- Remove opencode-go from _DOT_TO_HYPHEN_PROVIDERS (dots are correct for Go)
- Add opencode-go to _anthropic_preserve_dots() provider check
- Add opencode.ai/zen/go to base_url fallback check
- Add regression tests in tests/test_model_normalize.py

Co-authored-by: jacob3712 <jacob3712@users.noreply.github.com>

run_agent.py

@@ -5224,11 +5224,13 @@ class AIAgent:
         return transformed
 
     def _anthropic_preserve_dots(self) -> bool:
-        """True when using Alibaba/DashScope anthropic-compatible endpoint (model names keep dots, e.g. qwen3.5-plus)."""
-        if (getattr(self, "provider", "") or "").lower() == "alibaba":
+        """True when using an anthropic-compatible endpoint that preserves dots in model names.
+        Alibaba/DashScope keeps dots (e.g. qwen3.5-plus).
+        OpenCode Go keeps dots (e.g. minimax-m2.7)."""
+        if (getattr(self, "provider", "") or "").lower() in {"alibaba", "opencode-go"}:
             return True
         base = (getattr(self, "base_url", "") or "").lower()
-        return "dashscope" in base or "aliyuncs" in base
+        return "dashscope" in base or "aliyuncs" in base or "opencode.ai/zen/go" in base
 
     def _build_api_kwargs(self, api_messages: list) -> dict:
         """Build the keyword arguments dict for the active API mode."""