fix(voice): accept calls without conversation hydration; warn on refresh during ringing

- FloatingCallWidget: drop !conversation early-return in handleJoinCall —
  on a fresh account or after a hard refresh the inbound call's conversation
  may not be in the Vuex store yet, which silently no-op'd Accept while
  Reject worked (Reject doesn't read the conversation).
- useCallSession: seed the calls store from already-loaded voice_call
  messages with status='ringing' on mount and whenever the conversation
  list changes. Cable events (voice_call.incoming, message.created) are
  one-shot and not replayed on reconnect, so without seeding a refresh
  during a ringing call leaves the FloatingCallWidget empty.
- useCallSession: extend the beforeunload warning to fire while a call is
  ringing too — losing a ringing inbound to refresh is the same UX hit as
  losing an active one.

app/javascript/dashboard/components/widgets/FloatingCallWidget.vue

@@ -74,21 +74,25 @@ const handleEndCall = async () => {
 };
 
 const handleJoinCall = async call => {
+  if (!call || isJoining.value) return;
   const { conversation } = getCallInfo(call);
-  if (!call || !conversation || isJoining.value) return;
 
   // End current active call before joining new one
   if (hasActiveCall.value) {
     await handleEndCall();
   }
 
+  // After a hard refresh the conversation may not be hydrated yet — but the call
+  // object already carries inboxId from the cable / seeding path, so accept can
+  // proceed without it. Twilio still needs inboxId for initializeDevice; falls
+  // back to the conversation's inbox_id when present.
   const result = await joinCall({
     conversationId: call.conversationId,
-    inboxId: conversation.inbox_id,
+    inboxId: call.inboxId || conversation?.inbox_id,
     callSid: call.callSid,
   });
 
-  if (result) {
+  if (result && conversation) {
     router.push({
       name: 'inbox_conversation',
       params: { conversation_id: call.conversationId },