Add desktop tray widget + installer wizard

- Desktop widget (Python/pystray): system tray icon showing 5h usage as
  circular progress bar with Claude starburst logo, 10-step green-to-red
  color scale, right-click menu with usage stats and configuration
- Shared cache: both widget and CLI statusline read/write the same
  /tmp/claude_usage.json — only one fetcher needs to run
- Installer wizard (install_wizard.py): interactive cross-platform setup
  with component selection, session key prompt, cron/autostart config
- OS wrappers: install.sh (Linux/macOS) and install.ps1 (Windows) find
  Python 3.9+ and launch the wizard
- README with topology diagram, usage docs, and configuration reference

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,9 @@
+__pycache__/
+*.pyc
+*.pyo
+*.egg-info/
+dist/
+build/
+.venv/
+venv/
+node_modules/