Accessibility fixes and form session expiration fix

- Fix color contrast: change #179e83 to #148069 for WCAG AA compliance
- Add ARIA attributes to mobile nav toggle (aria-expanded, aria-controls)
- Implement focus trap on mobile menu with Escape key support
- Add aria-hidden to decorative hero SVG
- Add ARIA validation to contact form (aria-invalid, aria-describedby)
- Fix touch target sizes (notification close button 48x48px)
- Fix form session expiration by relaxing timestamp validation
- Add cache busting (v1.1.0) to JS/CSS files
- Update service worker cache version to force refresh

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

includes/header.php

@@ -18,10 +18,10 @@
             <a href="/#contact" class="nav-link">Contact</a>
             <a href="/quote" class="nav-link cta-button">Request Consultation</a>
         </div>
-        <div class="nav-toggle" id="nav-toggle">
+        <button class="nav-toggle" id="nav-toggle" aria-expanded="false" aria-controls="nav-menu" aria-label="Toggle navigation menu">
             <span class="bar"></span>
             <span class="bar"></span>
             <span class="bar"></span>
-        </div>
+        </button>
     </div>
 </nav>