feat: unified hook notifier, agent auto-detection, terminal transition UI

- Add hooks/notify.ps1 as single hook handler for all events
- Refactor settings.local.json to use notify.ps1 instead of inline PS
- Add Notification hook, auto-detect agent from session_id/transcript
- Rename agent 'main' to 'claude' across server routes and terminal
- Add loading overlay and error state for terminal switching transitions
- Add transitionError ref to useTranscriptDebug composable

server/routes/hooks-approval.ts

@@ -110,7 +110,7 @@ export async function handleHooksApprovalPermission(req: Request): Promise<Respo
     }))
 
     // Track in centralized session state → broadcasts patch to all clients
-    notifyAddApproval(body.agent_name || 'main', {
+    notifyAddApproval(body.agent_name || 'claude', {
       requestId,
       type: 'permission',
       toolName: body.tool_name,
@@ -189,7 +189,7 @@ export async function handleHooksApprovalPlan(req: Request): Promise<Response |
     }))
 
     // Track in centralized session state → broadcasts patch to all clients
-    notifyAddApproval('main', {
+    notifyAddApproval(body.agent_name || 'claude', {
       requestId,
       type: 'plan',
       lastAssistantText,