Add ability to delete individual conversations from history

Feature Request

Problem

There is currently no built-in way to delete individual conversations from Claude Code's session history. Users may want to remove specific conversations for cleanup, privacy, or organizational reasons.

Current Behavior

• Sessions are stored locally in ~/.claude/projects/<project-path>/sessions/
• Users can list sessions with claude --resume but cannot delete them
• The only workaround is manually finding and deleting session files from the filesystem

Proposed Solution

Add a command or option to delete specific conversations from history. Possible implementations:

1. CLI flag: claude --delete-session <session-id> to delete a specific session
2. Interactive deletion: Add a delete option in the claude --resume session picker (e.g., press d or Delete to remove a highlighted session)
3. Slash command: /delete-session to delete the current session and exit
4. Bulk cleanup: claude --clear-history to delete all sessions, or claude --clear-history --older-than 7d for time-based cleanup

Why This Matters

• Privacy: Users may want to remove sessions containing sensitive information
• Organization: Over time, session history accumulates and becomes harder to navigate
• Disk space: Long-running projects can accumulate many session files

Additional Context

Currently the only way to achieve this is by manually navigating the filesystem and deleting session files, which is error-prone and not user-friendly.