Session picker should display session names, dates, and IDs

Problem

The session picker (claude --resume / /resume) shows sessions by their first message rather than the name assigned via /rename. This makes /rename feel pointless and makes it hard to identify sessions at a glance.

There's also no --list flag to get a clean overview of sessions from the command line.

Current behavior

• /rename rails-7-migration names the session, but the picker still shows the first chat message as the identifier
• No way to list sessions with their names, IDs, and dates outside the interactive picker
• No way to programmatically reference sessions by name (e.g. claude --resume rails-7-migration doesn't reliably work)

Desired behavior

• Session picker should prominently display the assigned name (if set) instead of the first message
• A claude --list command (or similar) that outputs a clean table of sessions with: name, ID, date/time, branch, size
• Reliable resume-by-name support: claude --resume <name> should work with names set via /rename

Context

Session management is increasingly useful as users run multiple concurrent sessions, fork sessions, etc. But without clear naming/listing, it's hard to keep track of what's what.