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.

cli/src/world.rs

@@ -27,7 +27,7 @@ impl World {
         for dir in ["plugins", "state/core", "config"] {
             std::fs::create_dir_all(path.join(dir))?;
         }
-        std::fs::write(path.join("config/boot.json"), "[]\n")?;
+        std::fs::write(path.join("config/boot.yaml"), "[]\n")?;
         Self::open(path)
     }
     /// Return the folder that contains a plugin component.