[FEATURE]: Add Delete and Export options to the tab menu #56114

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

Problem Statement
Right-clicking a session tab shows only Rename and Close tab (packages/app/src/shell/titlebar/tab-nav.tsx:415-418).
The same session elsewhere already has Rename, Export…, Delete…:

• Home sessions list row menu (packages/app/src/home/sessions/view.tsx:782-789).
• Session timeline header More-options (packages/app/src/session/timeline/message-timeline.tsx:564-583).

Feature Requirement
Add Export… and Delete… to the tab menu.

Benefits

• No detour to Home or opening the session just to export/cleanup.
• Faster tab triage.
• Consistent expectations across the three menus (parity).

Acceptance Criteria

• Right-click tab shows the items in the order Rename, Export…, Delete…, ---,Close tab.
• Export saves JSON + toast, same as Home.
• Delete confirms, removes row from Home sessions list, closes the tab.
• Draft / session-less tab: Export/Delete disabled.

Related
#46113 created the 2-item tab menu
#43245 added the Home row actions
#50805 (open) touches the same tab-nav.tsx file