fix(frontend): offset error toast to prevent overlaying stop button (#1689)

This PR offsets the error toast to prevent it from annoyingly covering
the stop button within a chat. It also makes the toast dismissible so
that if it does get in the users way they can close it.

### Before
<img width="817" height="174" alt="Screenshot 2026-06-15 at 2 18 48 PM"
src="https://github.com/user-attachments/assets/20da4230-5400-4b9a-9258-ccc681f659e9"
/>

### After
<img width="817" height="174" alt="Screenshot 2026-06-15 at 2 15 16 PM"
src="https://github.com/user-attachments/assets/55d75d43-fd8b-4065-939c-2b1f7c0d11be"
/>


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

## Summary by CodeRabbit

* **Style**
* Toast notifications are now positioned in the bottom-right corner with
improved spacing and include a close button for user control.

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

Signed-off-by: Kyle Squizzato <kysquizz@redhat.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: squizzi

components/frontend/src/components/ui/sonner.tsx

@@ -17,6 +17,9 @@ const Toaster = ({ ...props }: ToasterProps) => {
     <Sonner
       theme={theme as ToasterProps["theme"]}
       className="toaster group"
+      position="bottom-right"
+      offset="80px"
+      closeButton
       icons={{
         success: <CircleCheckIcon className="size-4" />,
         info: <InfoIcon className="size-4" />,