feat(desktop,docs): surface stt.echo_transcripts in desktop settings and docs

Adapted from PR #53038 (stt.echo) to the stt.echo_transcripts key:
- desktop Voice settings section gains the Echo Transcripts toggle with
  label + description copy
- configuration.md documents stt.enabled / stt.echo_transcripts

apps/desktop/src/app/settings/constants.ts

@@ -335,6 +335,7 @@ export const FIELD_LABELS: Record<string, string> = defineFieldCopy({
   },
   stt: {
     enabled: 'Speech To Text',
+    echoTranscripts: 'Echo Transcripts',
     provider: 'Speech-To-Text Provider',
     local: {
       model: 'Local Transcription Model',
@@ -486,6 +487,7 @@ export const FIELD_DESCRIPTIONS: Record<string, string> = defineFieldCopy({
   },
   stt: {
     enabled: 'Enable local or provider-backed speech transcription.',
+    echoTranscripts: 'Post the raw 🎙️ transcript of voice messages back to the chat.',
     elevenlabs: {
       languageCode: 'Optional ISO-639-3 language code. Blank lets ElevenLabs auto-detect.'
     }
@@ -568,6 +570,7 @@ export const SECTIONS: DesktopConfigSection[] = [
     keys: [
       'tts.provider',
       'stt.enabled',
+      'stt.echo_transcripts',
       'stt.provider',
       'voice.auto_tts',
       'tts.edge.voice',

website/docs/user-guide/configuration.md

@@ -1543,6 +1543,8 @@ Hashes are deterministic — the same user always maps to the same hash, so the
 
 ```yaml
 stt:
+  enabled: true                # Auto-transcribe inbound voice messages (default: true)
+  echo_transcripts: true       # Post raw transcripts back to the chat as 🎙️ "..." (default: true)
   provider: "local"            # "local" | "groq" | "openai" | "mistral"
   local:
     model: "base"              # tiny, base, small, medium, large-v3
@@ -1551,6 +1553,8 @@ stt:
   # model: "whisper-1"         # Legacy fallback key still respected
 ```
 
+Set `stt.echo_transcripts: false` when the gateway should transcribe voice notes for the agent but must not post the raw transcript back to the chat (for example, customer-facing WhatsApp bots).
+
 Provider behavior:
 
 - `local` uses `faster-whisper` running on your machine. Install it separately with `pip install faster-whisper`.