feat: server-first terminal creation, broadcast-only WS clients

- Add POST /create-terminal endpoint with MAX_TERMINALS=5 limit
- Server creates PTY, runs command, registers and broadcasts atomically
- Frontend startTerminal() calls server first, connects in reconnect mode
- Remove registerTerminalOnServer() — server handles registration
- Separate broadcast-only WS clients from PTY clients (no phantom "main" PTY)
- All broadcast functions use broadcastToAll() helper
- Fix resume existing flow to create terminal with --resume flag

frontend/src/components/FloatingTranscriptDebug.vue

@@ -40,6 +40,9 @@ const {
   switchAgent,
   selectSession,
   createNewSession,
+  startTerminal,
+  parkCurrentTerminal,
+  fetchSessionContent,
   switchToTerminal,
   closeTerminal,
   disconnectRealtime,
@@ -468,7 +471,11 @@ async function handleModalResume(sessionId: string, agent: AgentName) {
   if (agent !== selectedAgent.value) {
     await switchAgent(agent)
   }
-  selectSession(sessionId)
+  // Load transcript + create terminal with --resume
+  parkCurrentTerminal()
+  selectedSessionId.value = sessionId
+  await fetchSessionContent(sessionId)
+  await startTerminal(sessionId)
 }
 
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