YAML configuration, init without a wizard, and openai-chat-completions

- /config/agent.yaml and /config/boot.yaml replace the JSON files, read
  with serde_yaml_ng (also in the agent, inside WASM).
- sausage init asks nothing and reads no SAUSAGE_* variables. It writes
  commented templates with an example for each API, and prints the path
  to edit. Until the agent is configured, agent.chat names the missing
  field. allow_no_token: true permits a local model without a key.
- The agent speaks openai-chat-completions, the format of OpenRouter,
  Ollama, and most providers. base_url follows each SDK: with /v1 for
  the OpenAI shapes, without it for Anthropic.
- Checked against the proxy with glm-5.3-flash: the agent wrote, built,
  and activated a counter plugin in 55 s.

sdk/src/lib.rs

@@ -199,7 +199,7 @@
 //! # A service with a fixed endpoint
 //!
 //! A service can publish a fixed path in `/run`. The core clears `/run` when the host starts.
-//! Configure this service in `/config/boot.json` with `{"method":"secrets.serve","params":{}}`.
+//! Configure this service in `/config/boot.yaml` with the entry `- method: secrets.serve`.
 //! Clients can then connect to `/run/secrets`.
 //!
 //! ```no_run