Feature Request: Add session rename functionality

Feature Request

Description

Add the ability to rename sessions with a custom display name for easier identification when resuming conversations.

Current Behavior

• Sessions are identified by firstPrompt and auto-generated summary in the session picker
• No way to assign a custom, memorable name to a session
• The sessions-index.json lacks a displayName or name field

Proposed Solution

1. Add /rename <name> slash command - Allow users to rename the current session

``
/rename auth-refactor
``

1. Add displayName field to session metadata in sessions-index.json:

``json
{
"sessionId": "xxx",
"displayName": "auth-refactor",
"firstPrompt": "...",
"summary": "..."
}
``

1. Support named resume - Allow resuming by name:

``bash
claude --resume auth-refactor
``

1. Add rename shortcut in session picker - Press R to rename highlighted session

Use Case

When working on multiple features/bugs across different sessions, it's difficult to find the right session to resume. Custom names like "payment-integration" or "auth-bug-fix" would be much easier to identify than auto-generated summaries.

Additional Context

• Similar to how terminal multiplexers (tmux) allow naming sessions
• Would significantly improve workflow for users managing multiple concurrent tasks