Add /restart command to restart session from within chat

Feature request

There's no way to restart a Claude Code session from within the chat. When settings change (e.g., permission mode, effort level) or the extension needs a fresh process, the only options are:

• Close and reopen the panel/tab
• Use VSCode command palette → "Developer: Reload Window" (restarts the entire VSCode window)
• /clear only clears history, doesn't restart the process

Proposed solution

Add a /restart slash command that:

1. Cleanly shuts down the current session process
2. Starts a new session with fresh settings
3. Preserves the tab/panel position in the UI

This would be especially useful when:

• Settings are changed mid-session (bypass permissions, effort level, etc.)
• The session is in a bad state (near context limit, MCP connection issues)
• After updating Claude Code to a new version

Environment

• Claude Code 2.1.76
• VSCode extension
• Running in devcontainer (Linux)