Improve text visibility in atom and dusk themes

- Add CSS variable support to dusk theme components for dynamic text colors
- Fix low-contrast preset color combinations (cyberpunk, neon, magma, forest, obsidian, space)
- Add text-shadow utility classes and apply to site header and backgrounds
- Style logout buttons as proper buttons matching other button styles
- Fix hardcoded text colors in atom theme components

resources/themes/atom/css/app.css

@@ -400,3 +400,13 @@ html.dark .badge-drawer-button .toggled {
   background-color: #fff;
   opacity: 0.1;
 }
+
+/* Text utility classes using CSS variables */
+.text-body { color: var(--color-text); }
+.text-muted { color: var(--color-text-muted); }
+.text-nav { color: var(--color-navbar-text); }
+
+/* Text shadow for readability */
+.text-shadow { text-shadow: 0 1px 3px rgba(0,0,0,0.8); }
+.text-shadow-sm { text-shadow: 0 1px 2px rgba(0,0,0,0.6); }
+.text-shadow-lg { text-shadow: 0 2px 8px rgba(0,0,0,0.9); }