feat: ResumeTerminalButton with ephemeral terminal for transcript-debug

- Add ResumeTerminalButton component with floating terminal modal
  (drag, resize, glass morphism, TerminalNavButtons bar)
- Add useEphemeralTerminal composable for temporary PTY sessions
  that auto-run `<agent> --resume <sessionId>` and cleanup on close
- Add /kill-session POST endpoint to terminal server for ephemeral
  session cleanup
- Integrate button in ChatContainer header (ID row) and status bar
- Pass selectedAgent to ChatContainer from TranscriptDebugPage

server/services/terminal.ts

@@ -276,6 +276,20 @@ export function startTerminalServer() {
         }
       }
 
+      // Kill a specific session by ID (used for ephemeral sessions)
+      if (url.pathname === '/kill-session' && req.method === 'POST') {
+        try {
+          const body = await req.json() as { sessionId: string }
+          if (!body.sessionId) {
+            return Response.json({ error: 'sessionId required' }, { status: 400, headers: corsHeaders })
+          }
+          const killed = killSession(body.sessionId)
+          return Response.json({ success: true, killed }, { headers: corsHeaders })
+        } catch (e: any) {
+          return Response.json({ error: e.message }, { status: 500, headers: corsHeaders })
+        }
+      }
+
       // Transcript update broadcast endpoint
       if (url.pathname === '/transcript-update' && req.method === 'POST') {
         try {