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>

hermes_cli/model_normalize.py

@@ -8,8 +8,9 @@ Different LLM providers expect model identifiers in different formats:
   hyphens: ``claude-sonnet-4-6``.
 - **Copilot** expects bare names *with* dots preserved:
   ``claude-sonnet-4.6``.
-- **OpenCode** (Zen & Go) follows the same dot-to-hyphen convention as
+- **OpenCode Zen** follows the same dot-to-hyphen convention as
   Anthropic: ``claude-sonnet-4-6``.
+- **OpenCode Go** preserves dots in model names: ``minimax-m2.7``.
 - **DeepSeek** only accepts two model identifiers:
   ``deepseek-chat`` and ``deepseek-reasoner``.
 - **Custom** and remaining providers pass the name through as-is.
@@ -67,7 +68,6 @@ _AGGREGATOR_PROVIDERS: frozenset[str] = frozenset({
 _DOT_TO_HYPHEN_PROVIDERS: frozenset[str] = frozenset({
     "anthropic",
     "opencode-zen",
-    "opencode-go",
 })
 
 # Providers that want bare names with dots preserved.