fix: increase API timeout default from 900s to 1800s for slow-thinking models (#3431)

Models like GLM-5/5.1 can think for 15+ minutes. The previous 900s
(15 min) default for HERMES_API_TIMEOUT killed legitimate requests.

Raised to 1800s (30 min) in both places that read the env var:
- _build_api_kwargs() timeout (non-streaming total timeout)
- _call_chat_completions() write timeout (streaming connection)

The streaming per-chunk read timeout (60s) and stale stream detector
(180-300s) are unchanged — those are appropriate for inter-chunk timing.

tests/test_run_agent.py

@@ -637,7 +637,7 @@ class TestBuildApiKwargs:
         kwargs = agent._build_api_kwargs(messages)
         assert kwargs["model"] == agent.model
         assert kwargs["messages"] is messages
-        assert kwargs["timeout"] == 900.0
+        assert kwargs["timeout"] == 1800.0
 
     def test_provider_preferences_injected(self, agent):
         agent.providers_allowed = ["Anthropic"]