Add keyboard shortcut to delete sessions from /resume picker

Feature Request

Add a keyboard shortcut (e.g., Ctrl+D or double-press Ctrl+D) to delete sessions directly from the /resume session picker.

Motivation

The /resume picker supports rename (R), preview (P), search (/), and filtering (A/B), but there's no way to delete old sessions. Over time the list gets cluttered and the only workaround is manually deleting .jsonl files from ~/.claude/projects/.

Proposed Behavior

• While navigating the session list in /resume, pressing a shortcut (e.g., Ctrl+D twice for safety) would delete the highlighted session.
• A confirmation prompt or the double-press requirement would prevent accidental deletion.

This would make session management much more convenient without leaving the CLI.