ui: add cross in the undo email toast, decrease time from 30s to 15s (#1979)

<!-- This is an auto-generated description by cubic. -->

## Summary by cubic
Added a close (cross) button to the undo email toast and reduced the undo window from 30 seconds to 15 seconds. 

- **UI Improvements**
 - The undo toast now shows a close button for quick dismissal.
 - The undo option is available for 15 seconds instead of 30.

<!-- End of auto-generated description by cubic. -->



<!-- This is an auto-generated comment: release notes by coderabbit.ai -->

## Summary by CodeRabbit

* **New Features**
  * Improved Undo experience: separate flows for scheduled vs. immediate sends with clearer toasts. Undoing a scheduled send cancels scheduling; undoing an immediate send restores the draft (including attachments) and reopens the composer. Toasts now last 15 seconds and include a close button.
  * Default delay before processing a send/schedule reduced from 30 seconds to 15 seconds.

* **Bug Fixes**
  * Prevented negative time remaining, ensuring Undo is reliably available and consistent with the 5-second gating.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

apps/mail/hooks/use-undo-send.ts

@@ -68,13 +68,31 @@ export const useUndoSend = () => {
     if (isSendResult(result) && settings?.settings?.undoSendEnabled) {
       const { messageId, sendAt } = result;
 
-      const timeRemaining = sendAt ? sendAt - Date.now() : 15_000;
+      const timeRemaining = sendAt ? Math.max(0, sendAt - Date.now()) : 15_000;
+      const wasUserScheduled = Boolean(emailData?.scheduleAt);
 
       if (timeRemaining > 5_000) {
-        toast.success('Email scheduled', {
-          action: {
-            label: 'Undo',
-            onClick: async () => {
+        if (wasUserScheduled) {
+          toast.success('Email scheduled', {
+            action: {
+              label: 'Undo',
+              onClick: async () => {
+                try {
+                  await unsendEmail({ messageId });
+                  toast.info('Schedule cancelled');
+                } catch {
+                  toast.error('Failed to cancel');
+                }
+              },
+            },
+            duration: 15_000,
+            closeButton: true,
+          });
+        } else {
+          toast.success('Email sent', {
+            action: {
+              label: 'Undo',
+              onClick: async () => {
               try {
                 await unsendEmail({ messageId });
                 
@@ -98,10 +116,12 @@ export const useUndoSend = () => {
               } catch {
                 toast.error('Failed to cancel');
               }
+              },
             },
-          },
-          duration: 15_000,
-        });
+            duration: 15_000,
+            closeButton: true,
+          });
+        }
       }
     }
   };

apps/server/src/trpc/routes/mail.ts

@@ -515,7 +515,7 @@ export const mailRouter = router({
 
           targetTime = parsedTime;
         } else {
-          targetTime = Date.now() + 30_000;
+          targetTime = Date.now() + 15_000;
         }
 
         const rawDelaySeconds = Math.floor((targetTime - Date.now()) / 1000);