Add persistent session color setting per project

Feature Request

Add a color setting to settings.json so that session color can be configured per-project and persists across sessions.

Use case

I work across multiple repositories and use /color to visually distinguish sessions by project. Currently, /color orange must be run manually at the start of every session. It would be great if this could be set once in .claude/settings.local.json (or .claude/settings.json) and applied automatically.

Proposed solution

Add a color field to the settings schema:

{
  "color": "orange"
}

This would be read at session start and applied automatically. Users could still override with /color during a session.

Alternatives considered

• SessionStart hook: Hooks can only run shell commands, not slash commands like /color, so this doesn't work today.
• Running /color manually each session: Works but is repetitive.