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>

install.ps1

@@ -0,0 +1,26 @@
+# Windows wrapper — launches the cross-platform installer wizard.
+# Usage: powershell -ExecutionPolicy Bypass -File install.ps1
+
+$ErrorActionPreference = "Stop"
+$ScriptDir = Split-Path -Parent $MyInvocation.MyCommand.Path
+
+# Find Python 3.9+
+$Python = $null
+foreach ($candidate in @("python3", "python")) {
+    $bin = Get-Command $candidate -ErrorAction SilentlyContinue
+    if ($bin) {
+        $version = & $bin.Source -c "import sys; print(f'{sys.version_info.major}.{sys.version_info.minor}')"
+        $parts = $version -split "\."
+        if ([int]$parts[0] -ge 3 -and [int]$parts[1] -ge 9) {
+            $Python = $bin.Source
+            break
+        }
+    }
+}
+
+if (-not $Python) {
+    Write-Error "Python 3.9+ is required to run the installer. Install Python 3.9+ and try again."
+    exit 1
+}
+
+& $Python (Join-Path $ScriptDir "install_wizard.py")