feat(homebridge-ring): expose Ring Alarm panel volume as a HomeKit slider (opt-in)

[salmanesm]

Closes #1652

Summary

Expose the Ring Alarm Base Station / Panel volume to HomeKit as a visible slider. This is opt-in and coexists with the existing Speaker/Volume characteristic.

Why

• Quick volume adjustments from the Home app (no need to open Ring).
• Enable scenes/automations (e.g., “Night” → quieter chimes).
• Keep defaults unchanged for users who don’t want the extra tile.

Implementation

• New accessory: VolumeAccessory
  • Uses Lightbulb service so the slider is prominent.
  • Maps Brightness (0–100) ↔ volume (0.0–1.0).
  • On = volume > 0; turning Off sets volume to 0.
  • Subscribes to device.onData to keep HomeKit in sync.
  • Gracefully handles devices without setVolume().
• Platform wiring: in ring-platform.ts, when exposeAlarmVolume is true, attach VolumeAccessory for devices that have data.volume and setVolume().
• Config: adds exposeAlarmVolume?: boolean (default false), and reserves volumeService?: 'lightbulb' | 'speaker' for future use.
• NodeNext-friendly imports: use explicit .ts extensions.

Behavior

• Default: no changes unless exposeAlarmVolume is enabled.
• When enabled, a new accessory like “<Panel Name> Volume” appears with a slider.
• Slider changes affect the device immediately; external volume changes reflect back in HomeKit.

Config example

{
  "platform": "Ring",
  "refreshToken": "<your-token>",
  "exposeAlarmVolume": true
}