Add Homebridge UI custom config, split devices into on_off/stateless sections, and UI assets

[pponce]

Motivation

• Provide a richer Homebridge Config UI X experience for Script2Platform by adding a custom UI and clearer separation of device types.
• Preserve legacy devices compatibility while encouraging a more structured on_off_switches and stateless_switches configuration shape.

Description

• Add a custom UI under homebridge-ui/ including index.html, index.js, and server.js and wire it into the plugin schema with customUi/customUiPath in config.schema.json.
• Update config.schema.json to expose on_off_switches, stateless_switches, and a conditional legacy devices array with validation, improved form layout, and helpful defaults/constraints.
• Revise README.md to document the new UI-driven sections, migration notes for legacy devices, examples, and an installation note; preserve backward compatibility guidance.
• Bump package version to 0.4.3-beta.27 and add @homebridge/plugin-ui-utils as a dependency required by the UI server.

Testing

• No automated tests were run for this change.

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Codex Task