Add session title/summary to --resume session list

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Currently, the --resume picker displays raw first messages like:

> Implement the following plan: ...
> ここでやっているデザインの改善を...

These are often long, truncated, and lack context, so it's hard to tell sessions apart at a glance.

Proposed Solution

Show a short auto-generated session title or summary alongside each session entry. For example:

1. [Slide design update] — 2h ago, 34 turns
2. [ATS data analysis for XXX] — 1d ago, 12 turns
3. [SSH agent troubleshooting] — 3d ago, 8 turns

The title could be generated by summarizing the first few exchanges (similar to how ChatGPT auto-titles conversations).

Alternative Solutions

• Manually crafting the first prompt to serve as a title — works but is a workaround
• claude --continue to resume the latest session — doesn't help when switching between multiple sessions

Priority

High - Significant impact on productivity

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

_No response_