Feature request: project-level sessionColor setting

Problem

/color sets a session color but resets every session. There's no way to persist it.

Different projects benefit from different colors (e.g., blue for notes, red for production infra, green for dev). Currently you have to type /color blue at the start of every session.

Proposed solution

Add a sessionColor setting that works at all configuration scopes (user, project, local):

// .claude/settings.json (project level)
{
  "sessionColor": "blue"
}

When set, the session starts with that color automatically. Project-level settings would let teams/repos have distinct visual identifiers. User-level would set a personal default.

Alternatives considered

• SessionStart hook: hooks can only run shell commands, not CC slash commands
• Typing /color manually each session: works but defeats the purpose of configuration

Additional context

This is a small quality-of-life improvement for users who work across multiple projects/repos and use color to visually distinguish contexts.