feat(mcp): add MCP Gateway integration for all LifeSmart device types

Add mcp.py platform module that exposes LifeSmart devices via mcp_gateway.
Each device gets its own MCP server with tools matching its capabilities,
directly invoking the LifeSmart client for control operations.

Supported device types:
- Hub: trigger_scene, get_scene_list
- Switch: turn_on, turn_off, get_state (all switch/plug types)
- Light: basic on/off, brightness, color temp, RGB, RGBW, SPOT, quantum
- Climate: turn_on/off, set_temperature, set_hvac_mode, set_fan_mode
- Cover: open, close, stop, set_position (positional + non-positional)
- Sensor: get_state (temperature, humidity, power, etc.)
- Binary Sensor: get_state (door/window, motion, smoke, etc.)

Includes HA version compatibility shim for llm module (2024.6+).

Author: abcsnowwolf