fix: preserve dots in model names for OpenCode Zen and ZAI providers (#8794)

OpenCode Zen was in _DOT_TO_HYPHEN_PROVIDERS, causing all dotted model
names (minimax-m2.5-free, gpt-5.4, glm-5.1) to be mangled. The fix:

Layer 1 (model_normalize.py): Remove opencode-zen from the blanket
dot-to-hyphen set. Add an explicit block that preserves dots for
non-Claude models while keeping Claude hyphenated (Zen's Claude
endpoint uses anthropic_messages mode which expects hyphens).

Layer 2 (run_agent.py _anthropic_preserve_dots): Add opencode-zen and
zai to the provider allowlist. Broaden URL check from opencode.ai/zen/go
to opencode.ai/zen/ to cover both Go and Zen endpoints. Add bigmodel.cn
for ZAI URL detection.

Also adds glm-5.1 to ZAI model lists in models.py and setup.py.

Closes #7710

Salvaged from contributions by:
- konsisumer (PR #7739, #7719)
- DomGrieco (PR #8708)
- Esashiero (PR #7296)
- sharziki (PR #7497)
- XiaoYingGee (PR #8750)
- APTX4869-maker (PR #8752)
- kagura-agent (PR #7157)

tests/agent/test_minimax_provider.py

@@ -308,6 +308,34 @@ class TestMinimaxPreserveDots:
         from run_agent import AIAgent
         assert AIAgent._anthropic_preserve_dots(agent) is False
 
+    def test_opencode_zen_provider_preserves_dots(self):
+        from types import SimpleNamespace
+        agent = SimpleNamespace(provider="opencode-zen", base_url="")
+        from run_agent import AIAgent
+        assert AIAgent._anthropic_preserve_dots(agent) is True
+
+    def test_opencode_zen_url_preserves_dots(self):
+        from types import SimpleNamespace
+        agent = SimpleNamespace(provider="custom", base_url="https://opencode.ai/zen/v1")
+        from run_agent import AIAgent
+        assert AIAgent._anthropic_preserve_dots(agent) is True
+
+    def test_zai_provider_preserves_dots(self):
+        from types import SimpleNamespace
+        agent = SimpleNamespace(provider="zai", base_url="")
+        from run_agent import AIAgent
+        assert AIAgent._anthropic_preserve_dots(agent) is True
+
+    def test_bigmodel_cn_url_preserves_dots(self):
+        from types import SimpleNamespace
+        agent = SimpleNamespace(provider="custom", base_url="https://open.bigmodel.cn/api/paas/v4")
+        from run_agent import AIAgent
+        assert AIAgent._anthropic_preserve_dots(agent) is True
+
+    def test_normalize_preserves_m25_free_dot(self):
+        from agent.anthropic_adapter import normalize_model_name
+        assert normalize_model_name("minimax-m2.5-free", preserve_dots=True) == "minimax-m2.5-free"
+
     def test_normalize_preserves_m27_dot(self):
         from agent.anthropic_adapter import normalize_model_name
         assert normalize_model_name("MiniMax-M2.7", preserve_dots=True) == "MiniMax-M2.7"