Allow per-project color and display-name override in .claude/config.json

The session header in Claude Code renders the project name as a colored chip (e.g., "WIN" in green, "Radon" in orange). The color appears to be auto-derived from a hash of the project name, with no documented way to override.

Request: support per-project customization via .claude/config.json:

{
  "display": {
    "name": "WIN",
    "color": "green"
  }
}

• display.name overrides the chip text (today defaults to the directory name)
• display.color overrides the chip color (today auto-derived from the project name)

Why: users who run many concurrent sessions across many projects benefit from consistent visual identity per project. A health-related project should always be pink, a money/accounting project always green, a brand client always royal blue. The current auto-hash gives stable colors but no influence — projects with semantically-related themes get arbitrarily unrelated colors, which adds friction for users juggling 5–10+ open sessions.

Color values: accept either CSS color names (red, green, blue, pink, brown, orange, teal, gold, royalblue, etc.) or hex codes (e.g., #3B82F6).

Backward compatibility: if .claude/config.json is missing or has no display key, fall back to current auto-hash behavior. No behavior change for existing users.

Bonus consideration: if display.name is set, it could also influence the terminal window title and the project listing in any future project-switcher UI — making the override a single source of truth for "how this project appears."