fix: prevent duplicate session action requests causing 404s

- Add early return guards in all session action handlers (start, stop, delete, recreate tunnel)
- Prevents race conditions where double-clicks or rapid clicks fire duplicate API calls
- First delete succeeds, second would 404 because instance is already deleted
- Applied to both sessions page and dashboard/home page

apps/web/src/pages/dashboard.tsx

@@ -143,6 +143,7 @@ export const HomePage = () => {
   };
 
   const handleStop = async (session: SessionView) => {
+    if (actionBusy === session.id) return;
     setActionBusy(session.id);
     try {
       await stopInstance(session.project_id, session.repository_id, session.id);
@@ -153,6 +154,7 @@ export const HomePage = () => {
   };
 
   const handleDelete = async (session: SessionView) => {
+    if (actionBusy === session.id) return;
     setActionBusy(session.id);
     try {
       await deleteInstance(session.project_id, session.repository_id, session.id);
@@ -165,6 +167,7 @@ export const HomePage = () => {
   };
 
   const handleRecreateTunnel = async (session: SessionView) => {
+    if (actionBusy === session.id) return;
     setActionBusy(session.id);
     try {
       await recreateInstanceTunnel(session.project_id, session.repository_id, session.id);
@@ -175,6 +178,7 @@ export const HomePage = () => {
   };
 
   const handleStart = async (session: SessionView) => {
+    if (actionBusy === session.id) return;
     setActionBusy(session.id);
     try {
       await startInstance(session.project_id, session.repository_id, session.id);