v0.23.0

Added

• OpenRouter provider: new daimon-provider-openrouter crate behind the
  openrouter feature (also in full). OpenRouter implements Model
  against OpenRouter's OpenAI-compatible Chat Completions API — one API key
  (OPENROUTER_API_KEY) for hundreds of models in vendor/model form
  (e.g. openai/gpt-4o, anthropic/claude-sonnet-4). Supports streaming,
  tool calls, retries with exponential backoff, with_response_format,
  with_parallel_tool_calls, and the HTTP-Referer/X-Title attribution
  headers via with_site_url/with_app_name. Facade re-export at
  daimon::model::openrouter; new openrouter_agent example.