Add Umami custom event tracking across all key pages

- Created /js/pw-analytics.js with conversion funnel events
- Added to Base.astro layout (all Astro pages) + 6 static HTML pages
- Events tracked: compliance-check-start, compliance-check-complete,
  order-cta-click, checkout-page-view, checkout-start, esign-opened,
  esign-submitted, campaign-click (UTM attribution), contact-form-submit
- Server-side payment-complete event from checkout webhook via Umami API
- Auto-tracks any element with data-track="event-name" attribute

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

site/src/layouts/Base.astro

@@ -31,6 +31,8 @@ try {
     <title>{title} | Performance West Inc.</title>
     {description && <meta name="description" content={description} />}
     <link rel="icon" type="image/svg+xml" href="/favicon.svg" />
+    <script defer src="https://analytics.performancewest.net/script.js" data-website-id="55250014-ee15-44ac-a1f6-81dabad3fe0f"></script>
+    <script defer src="/js/pw-analytics.js"></script>
     <link rel="preconnect" href="https://fonts.googleapis.com" />
     <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
     <link href="https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&family=JetBrains+Mono:wght@400;500&display=swap" rel="stylesheet" />