Add ability to delete conversations from /resume picker

Feature Request

Add the ability to delete old conversations directly from the /resume command interface.

Problem

Currently, /resume only allows selecting and resuming past conversations. There's no way to clean up old or unwanted conversations from within the picker. Users who want to remove stale sessions must manually delete .jsonl files from ~/.claude/projects/.

Proposed Solution

Add a keybinding (e.g., Ctrl+D or Del) within the /resume conversation picker that allows deleting the currently highlighted conversation. A confirmation prompt before deletion would prevent accidental removals.

Benefits

• Keeps the /resume list manageable over time
• No need to manually navigate the filesystem to clean up conversations
• Better UX for users who work across many projects/sessions