feat(compression): add summary_base_url + move compression config to YAML-only

- Add summary_base_url config option to compression block for custom
  OpenAI-compatible endpoints (e.g. zai, DeepSeek, Ollama)
- Remove compression env var bridges from cli.py and gateway/run.py
  (CONTEXT_COMPRESSION_* env vars no longer set from config)
- Switch run_agent.py to read compression config directly from
  config.yaml instead of env vars
- Fix backwards-compat block in _resolve_task_provider_model to also
  fire when auxiliary.compression.provider is 'auto' (DEFAULT_CONFIG
  sets this, which was silently preventing the compression section's
  summary_* keys from being read)
- Add test for summary_base_url config-to-client flow
- Update docs to show compression as config.yaml-only

Closes #1591
Based on PR #1702 by @uzaylisak

hermes_cli/config.py

@@ -162,6 +162,7 @@ DEFAULT_CONFIG = {
         "threshold": 0.50,
         "summary_model": "google/gemini-3-flash-preview",
         "summary_provider": "auto",
+        "summary_base_url": None,
     },
     "smart_model_routing": {
         "enabled": False,