New system integration that owns the LLM tools platform: its async_setup
drives async_process_integration_platforms(hass, "llm", ...) so integrations
can ship an <integration>/llm.py with an async_setup_tools hook to register
tools, mirroring the intent helper/integration split. The framework (registry,
Tool, APIs) stays in homeassistant.helpers.llm. No tools are registered yet,
so behavior is unchanged.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>