feat: centralize session state on terminal server

- Add SessionStateManager (server/services/session-state.ts) as source
  of truth for agent status, tools, approvals, and notifications
- Integrate into terminal server with state patches broadcast via WS
- Add /add-approval and /resolve-approval endpoints so approval
  lifecycle is tracked centrally and broadcast to all clients
- Add permissionMode field to AgentSessionState
- Frontend store (session-state.ts) + WS service (session-state-ws.ts)
  consume snapshots and patches from terminal server (4103)
- Rewrite useGlobalApproval to derive pending approvals from
  centralized state — resolving on one client now clears all others
- Migrate useTranscriptDebug: processing, hookMeta, serverRegistry
  now derived from session state store; remove 5s registry polling
- hooks-approval.ts notifies terminal server on add/resolve

frontend/src/components/FloatingTranscriptDebug.vue

@@ -435,7 +435,7 @@ function openAtCursor(x: number, y: number) {
   })
 }
 
-defineExpose({ openAtCursor })
+defineExpose({ openAtCursor, openTerminals, activeTerminalSessionId, switchToTerminal })
 
 function handleAgentSwitch(agent: AgentName) {
   switchAgent(agent)
@@ -523,6 +523,7 @@ onMounted(async () => {
   oceanLifeTimer = setInterval(tickOceanLife, 20000)
   tickOceanLife()
   await voice.init()
+  // Terminal registry is now synced via centralized session state WS (no polling needed)
 })
 
 onBeforeUnmount(() => {