feat: add project-theme plugin for per-project theme settings

[12britz]

Summary

Adds a plugin that reads theme settings from .claude/settings.json and automatically applies them on session start, solving the per-project persistent color/theme request.

Closes #43216

What this does

• Adds a SessionStart hook that reads theme or color from project settings
• Supports both .claude/settings.json (project) and .claude/settings.local.json (local override)
• Uses jq for proper JSON parsing when available, falls back to grep
• Outputs a theme command that Claude Code processes

Usage

Add to your project's .claude/settings.json:

{
  "theme": "pink"
}

Or use .claude/settings.local.json for local overrides:

{
  "color": "blue"
}

Supported Values

Any theme name supported by Claude Code's /theme command:

• dark, light, light-ansi, dark-ansi
• pink, blue, green, orange, purple, red, yellow
• Custom theme names from ~/.claude/themes/

How it works

1. On SessionStart, the hook reads settings files (local takes precedence)
2. Extracts theme or color value using jq or grep fallback
3. Outputs a JSON command that Claude Code processes to apply the theme

Files

• plugins/project-theme/plugin.json - Plugin manifest
• plugins/project-theme/hooks/apply-theme.sh - SessionStart hook
• plugins/project-theme/README.md - Documentation
• plugins/project-theme/examples/.claude/settings.json - Example config

Testing

# Test the hook directly
cd examples && bash ../hooks/apply-theme.sh
# Output: Applying project theme: pink
# Output: {"type": "theme", "theme": "pink"}