fix: Remove transparency from mobile buttons and fix landscape layout

Mobile Button Opacity (No Transparency):
- Changed all mobile button backgrounds from rgba(x,x,x,0.5) to rgba(x,x,x,1)
- Added opacity: 1 !important to override base opacity: 0.6 rules
- Buttons now display at full opacity with iOS blur bar backdrop
- Affected buttons: download, print-friendly, shortcuts, info, back-to-top, theme-switcher

Landscape Layout Fix:
- Added single-column grid rule for landscape orientation
- Media query: @media (max-width: 915px) and (orientation: landscape)
- Forces grid-template-columns: 1fr for both page-1 and page-2
- Prevents 2-column layout on iPhone landscape (844px wide)

Files Modified:
- static/css/04-interactive/_scroll-behavior.css: Button opacity overrides
- static/css/05-responsive/_breakpoints.css: Landscape single-column grid
- static/css/color-theme.css: Theme switcher opacity override

Visual Changes:
- Mobile buttons: Full color, no transparency (vibrant appearance)
- Landscape: Single column layout (sidebar top, content below)
- Maintains footer-hovered transparency for footer interaction

static/css/04-interactive/_scroll-behavior.css

@@ -132,13 +132,15 @@
         transform: none !important;
     }
 
-    /* Mobile: Show colors at 50% transparency by default */
+    /* Mobile: Show colors at full opacity (no transparency with blur bar) */
     .download-btn {
-        background: rgba(205, 96, 96, 0.5) !important; /* PDF red at 50% */
+        background: rgba(205, 96, 96, 1) !important; /* PDF red - full opacity */
+        opacity: 1 !important; /* Override base opacity */
     }
 
     .print-friendly-btn {
-        background: rgba(255, 255, 255, 0.5) !important; /* White at 50% */
+        background: rgba(255, 255, 255, 1) !important; /* White - full opacity */
+        opacity: 1 !important; /* Override base opacity */
     }
 
     .print-friendly-btn iconify-icon {
@@ -146,16 +148,18 @@
     }
 
     .shortcuts-btn {
-        background: rgba(243, 156, 18, 0.5) !important; /* Orange at 50% */
+        background: rgba(243, 156, 18, 1) !important; /* Orange - full opacity */
+        opacity: 1 !important; /* Override base opacity */
     }
 
     .info-button {
-        background: rgba(39, 174, 96, 0.5) !important; /* Green at 50% */
+        background: rgba(39, 174, 96, 1) !important; /* Green - full opacity */
+        opacity: 1 !important; /* Override base opacity */
     }
 
     .back-to-top {
-        background: rgba(39, 174, 96, 0.5) !important; /* Green at 50% */
-        opacity: 0.5; /* Semi-transparent by default, full opacity when at-bottom */
+        background: rgba(39, 174, 96, 1) !important; /* Green - full opacity */
+        opacity: 1 !important; /* Full opacity (no transparency with blur bar) */
     }
 
     /* Flexbox container behavior - buttons arrange themselves */