fix: gate Intercom on server-side hasCommand instead of microphone/speaker props

[retrography]

Summary

Some doorbells that support two-way talk — notably Video Doorbell S220 (BATTERY_DOORBELL_2) — do not expose microphone or speaker boolean properties on the underlying eufy-security device. The current gate in createDeviceManifest (device-utils.ts:288-293) requires both properties to be present, so for these models the Intercom interface is never added and HomeKit / Scrypted hide the talk button.

Replace the property-presence check with a server-side api.hasCommand("deviceStartTalkback") call, which consults the authoritative DeviceCommands table in eufy-security-client. This is the same source of truth the server uses when actually executing talkback, so the manifest now matches what the device will accept at runtime.

Repro

• Device: Eufy Video Doorbell S220 (T8210, BATTERY_DOORBELL_2)
• Connected via eufy-security-ws to caplaz/eufy-security-scrypted, exported to HomeKit
• Live video works, motion + doorbell press fire correctly
• Talk button absent in HomeKit; device.interfaces in the Scrypted REPL does not include Intercom

getProperties for the S220 returns a payload that does not include microphone or speaker (confirmed against the upstream property table for BATTERY_DOORBELL_2), so the properties.microphone !== undefined && properties.speaker !== undefined gate evaluates false and Intercom is skipped — even though the upstream DeviceCommands table for this model does include CommandName.DeviceStartTalkback.

Fix

// The argument is the upstream CommandName enum value (camelCase), not the
// snake_case WS protocol command name.
const { exists: hasTalkback } = await api.hasCommand("deviceStartTalkback");
if (hasTalkback) {
  interfaces.push(ScryptedInterface.Intercom);
}

Note on the string: api.hasCommand proxies to Device.hasCommand upstream, which checks the value against the CommandName enum — those values are camelCase ("deviceStartTalkback"), not the snake-case WS protocol command name ("device.start_talkback" from DEVICE_COMMANDS.START_TALKBACK). It would be nice to export the CommandName enum from @caplaz/eufy-security-client so callers don't have to hard-code the string, but that's out of scope for this fix.

Tests

Updated tests/unit/device-utils.test.ts:

• ✅ Intercom added when device supports deviceStartTalkback
• ✅ Intercom added when talkback is supported but microphone/speaker properties are absent (the S220 case)
• ✅ Intercom NOT added when device does not support deviceStartTalkback, even if microphone + speaker properties are present

All 11 tests in device-utils.test.ts pass.

Test plan

• npm test -- device-utils.test.ts passes locally
• Lint + format pass (pre-commit hook)
• Verified on hardware: device.interfaces now includes Intercom for an S220, and the HomeKit talk button works