Add Homebridge Config UI (custom UI) with on_off/stateless config schema and UI frontend

[pponce]

Motivation

• Provide a native Homebridge Config UI X experience for Script2 and split legacy devices into clear on_off_switches and stateless_switches sections while preserving backward compatibility.
• Make it easier to add and manage switches via a visual editor instead of editing raw JSON.
• Ship a minimal custom UI and server so the plugin can render a friendly configuration page in Homebridge UI.

Description

• Added a custom UI for the plugin under homebridge-ui/ including public/index.html, public/index.js, and a small UI server server.js using @homebridge/plugin-ui-utils.
• Updated config.schema.json to declare customUi and customUiPath, add on_off_switches and stateless_switches array schemas, and keep a conditional legacy devices array for compatibility.
• Updated README.md to document the new configuration shape, provide migration notes and examples for on_off_switches / stateless_switches, and add an Installation section.
• Bumped package version and added @homebridge/plugin-ui-utils to dependencies in package.json.

Testing

• No automated tests were added or executed as part of this change.

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Codex Task