fix: Remove unused cookie helper functions and fix desktop sidebar visibility

1. Removed unused getPreferenceCookie and setPreferenceCookie functions
   - These were flagged by golangci-lint as unused
   - Cookie preferences now handled client-side via localStorage
   - Removed unused net/http import

2. Fixed desktop sidebar accordion auto-opening
   - Updated handleLandscapeAccordions() to open accordions in desktop view (≥769px)
   - Sidebars now show content in desktop, landscape mobile, and portrait mobile
   - Only keep accordions collapsed in portrait mobile for space saving

3. Created comprehensive multi-viewport test (66-comprehensive-all-viewports-test.mjs)
   - Tests desktop (1278px), portrait mobile (375×667), landscape mobile (667×375)
   - Validates sidebars, accordion state, content visibility, AND all buttons
   - Checks button backdrop visibility in mobile views
   - Every feature now has corresponding test coverage

Fixes golangci-lint errors:
- internal/handlers/cv_helpers.go:366: func getPreferenceCookie is unused
- internal/handlers/cv_helpers.go:375: func setPreferenceCookie is unused
- internal/handlers/cv_helpers.go:7: net/http imported and not used

static/js/main.js

@@ -74,32 +74,38 @@
     };
 
     /**
-     * Auto-open sidebar accordions in landscape mobile mode
-     * Ensures sidebar content is visible in landscape orientation
+     * Auto-open sidebar accordions in landscape mobile mode AND desktop
+     * Ensures sidebar content is always visible except in portrait mobile
      */
     function handleLandscapeAccordions() {
-        function openSidebarAccordionsIfLandscape() {
+        function openSidebarAccordionsIfNeeded() {
             const isLandscape = window.matchMedia('(max-width: 915px) and (orientation: landscape)').matches;
+            const isDesktop = window.matchMedia('(min-width: 769px)').matches;
+            const isPortraitMobile = window.matchMedia('(max-width: 768px) and (orientation: portrait)').matches;
 
-            if (isLandscape) {
-                // Open all sidebar accordions in landscape mode
+            // Open accordions in landscape mobile OR desktop view
+            // Keep them closed ONLY in portrait mobile (≤768px)
+            if (isLandscape || isDesktop) {
                 document.querySelectorAll('.sidebar-accordion').forEach(accordion => {
                     accordion.setAttribute('open', '');
                 });
+            } else if (isPortraitMobile) {
+                // In portrait mobile, leave them closed (user can expand manually)
+                // Don't remove 'open' attribute if user has opened them
             }
         }
 
         // Run on load
-        openSidebarAccordionsIfLandscape();
+        openSidebarAccordionsIfNeeded();
 
         // Run on orientation change
         window.addEventListener('orientationchange', () => {
-            setTimeout(openSidebarAccordionsIfLandscape, 100);
+            setTimeout(openSidebarAccordionsIfNeeded, 100);
         });
 
         // Run on resize (for desktop browser testing)
         window.addEventListener('resize', () => {
-            openSidebarAccordionsIfLandscape();
+            openSidebarAccordionsIfNeeded();
         });
     }