feat(providers): extend request_timeout_seconds to all client paths

Follow-up on top of mvanhorn's cherry-picked commit. Original PR only
wired request_timeout_seconds into the explicit-creds OpenAI branch at
run_agent.py init; router-based implicit auth, native Anthropic, and the
fallback chain were still hardcoded to SDK defaults.

- agent/anthropic_adapter.py: build_anthropic_client() accepts an optional
  timeout kwarg (default 900s preserved when unset/invalid).
- run_agent.py: resolve per-provider/per-model timeout once at init; apply
  to Anthropic native init + post-refresh rebuild + stale/interrupt
  rebuilds + switch_model + _restore_primary_runtime + the OpenAI
  implicit-auth path + _try_activate_fallback (with immediate client
  rebuild so the first fallback request carries the configured timeout).
- tests: cover anthropic adapter kwarg honoring; widen mock signatures
  to accept the new timeout kwarg.
- docs/example: clarify that the knob now applies to every transport,
  the fallback chain, and rebuilds after credential rotation.

tests/hermes_cli/test_model_switch_opencode_anthropic.py

@@ -214,7 +214,7 @@ class TestAgentSwitchModelDefenseInDepth:
         # client factory.
         captured = {}
 
-        def _fake_build_anthropic_client(api_key, base_url):
+        def _fake_build_anthropic_client(api_key, base_url, **kwargs):
             captured["api_key"] = api_key
             captured["base_url"] = base_url
             return object()  # placeholder client — no real calls expected
@@ -226,7 +226,7 @@ class TestAgentSwitchModelDefenseInDepth:
         class _Sentinel(Exception):
             pass
 
-        def _raise_after_capture(api_key, base_url):
+        def _raise_after_capture(api_key, base_url, **kwargs):
             captured["api_key"] = api_key
             captured["base_url"] = base_url
             raise _Sentinel("strip verified")