[FEATURE] Support project-level session color configuration

Feature Request

Add support for a project-level session color/accent setting so that each project automatically gets a distinct visual appearance whenever a new Claude Code session is opened in that directory.

Use case

When working across multiple projects, it's easy to lose track of which Claude Code session belongs to which project — especially after restarting the machine or reopening sessions. A per-project color would provide an instant visual cue.

Suggested implementation

Allow a sessionColor (or similar) key in the project-level .claude/settings.json:

{
  "sessionColor": "blue"
}

This would set the accent/theme color for any Claude Code session opened in that project directory, persisting across restarts and new sessions.

Current workaround

The custom status line can display colored text per project via a shell script with ANSI escape codes, but this only affects the status bar — not the overall session theme.