Add /rename command to VSCode extension

Feature Request: Add /rename command to VSCode extension

Is your feature request related to a problem?

Yes. The CLI version of Claude Code supports session naming via:

• claude -n "session name" at startup
• /rename <name> during an active session

However, neither option exists in the VSCode extension. When working with multiple sessions, the only way to rename them is through the UI (hovering over a session in "Past Conversations" and clicking the pencil icon). This is cumbersome when you want to name a session while working.

Describe the solution you'd like

Add the /rename command to the VSCode extension with the same behavior as the CLI:

/rename Add Switch Firmware versions

This would set the session's display name so it appears in the session picker with a descriptive title instead of an auto-generated one.

Describe alternatives you've considered

1. Custom slash command — Not possible because .claude/commands/*.md files are prompt injections that can't access the VSCode extension's session state
2. Hooks — No hook event exposes session naming
3. Manual UI rename — Works but breaks flow when you're in the middle of work

Additional context

This would help users who:

• Work on multiple features simultaneously across sessions
• Resume sessions days later and need descriptive names to find the right one
• Prefer keyboard-driven workflows over mouse interactions

The session naming infrastructure already exists (visible in "Past Conversations"). This request is just to expose it via the /rename slash command like the CLI does.