[FEATURE]: Add delete button for sessions in sidebar #33129

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

What do you want to change or add?

Add a delete (trash) icon button next to the existing archive button on every root session row in the project/session sidebar.

Clicking the trash icon should open a confirmation dialog. After confirming, the app calls the existing client.session.delete API to permanently remove the session. If the deleted session is currently active, the user should be redirected to the next session or to the new-session view.

What are the benefits of implementing this?

Right now the sidebar only lets users archive sessions. Archiving hides them but keeps the data around, so there is no quick way to clean up old sessions directly from the sidebar. Users must open a session and delete it from the timeline menu instead.

Adding a delete button next to archive makes session management more complete, reduces the number of clicks, and keeps the sidebar actions consistent with the delete option already available inside the session timeline.

Acceptance Criteria

• A delete (trash) icon appears next to the archive icon when hovering a session row (and on mobile).
• Clicking delete opens a confirmation dialog.
• Confirming calls the existing session.delete API.
• On success, the session is removed from the list and, if it was active, the user is redirected to the next session or the new-session view.
• Error case shows the existing "Failed to delete session" toast.

Additional Context

The trash icon already exists in @opencode-ai/ui/icon, and the session.delete endpoint plus i18n strings are already implemented.

I have verified this feature I'm about to request hasn't been suggested before.

• I have checked existing issues.