feat: add delete session button to session header

[usvimal]

Summary

Adds a delete button in the session header for quick session cleanup.

Changes

• Added X icon button next to the "New session" button
• Shows confirmation dialog before deletion
• Navigates to new session page after successful deletion
• Button only visible when a session is selected

UI Location

[Project ▾] / [Session ▾]  [✏️ New]  [✕ Delete]

Testing

• Click delete button on any session
• Confirm deletion in dialog
• Session should be deleted and redirected to new session page