chore(voice): trim dead exports, fix duplicate-OR bug, drop redundant comments

Branch review pass:
- useWhatsappCallSession: drop unused `error` ref and unused exports
  (hasActiveWhatsappCall, isWhatsappCallMuted), fold sendWhatsappCallBeacon
  into a private beaconTerminate helper since only sendWhatsappTerminateBeacon
  consumed it externally. Trim WHAT-comments; keep WHY-comments
  (browser-quirk explanations, race-condition notes, auth-cookie rationale).
- VoiceCall.vue bubble: fix `data || data` short-circuit that did nothing —
  upstream key transform was the same on both branches; collapse to one read.
- calls/useCallSession/actionCable/FloatingCallWidget/VoiceCallButton:
  drop comments that just describe what the next line already says.

Net diff: -63 lines across 7 files. No behavior change.

app/javascript/dashboard/helper/actionCable.js

@@ -40,8 +40,6 @@ class ActionCableConnector extends BaseActionCableConnector {
       'account.cache_invalidated': this.onCacheInvalidate,
       'account.enrichment_completed': this.onEnrichmentCompleted,
       'copilot.message.created': this.onCopilotMessageCreated,
-      // WhatsApp call SDP exchange happens via these events; Twilio-shaped voice_call.*
-      // events also flow through here but are ignored when provider !== 'whatsapp'.
       'voice_call.incoming': this.onVoiceCallIncoming,
       'voice_call.outbound_connected': this.onVoiceCallOutboundConnected,
       'voice_call.ended': this.onVoiceCallEnded,
@@ -228,8 +226,6 @@ class ActionCableConnector extends BaseActionCableConnector {
       provider: 'whatsapp',
       sdpOffer: data.sdp_offer,
       iceServers: data.ice_servers,
-      // Caller info for the FloatingCallWidget so it doesn't show "Unknown caller"
-      // before the conversation/contact has loaded into the store.
       caller: data.caller,
     });
   };
@@ -243,13 +239,12 @@ class ActionCableConnector extends BaseActionCableConnector {
   // eslint-disable-next-line class-methods-use-this
   onVoiceCallEnded = async data => {
     if (data?.provider !== 'whatsapp') return;
-    // Must await the upload-and-cleanup BEFORE removeCall, because the store's
-    // sync teardownByProvider -> cleanupWhatsappSession would otherwise wipe
-    // mediaRecorder + recorderChunks before any upload microtask gets to run.
+    // Await upload before removeCall — the store's sync teardown would otherwise
+    // wipe the recorder chunks before they reach the server.
     try {
       await handleWhatsappRemoteEnd(data.id);
     } catch (_) {
-      /* noop — upload is best-effort */
+      /* noop */
     }
     useCallsStore().removeCall(data.call_id);
   };