fix: Theme-aware sidebar with dark mode support

Light theme sidebar:
- Background: #d1d4d2 (light gray)
- Text: dark colors

Dark theme sidebar:
- Background: #3a3d3e (darker gray, between page bg and content)
- Text: light colors (using CSS variables)
- Titles: light colors

Changes:
- Revert sidebar bg to use var(--sidebar-bg) for theme switching
- Update dark theme sidebar color to #3a3d3e
- Replace all hardcoded text colors with CSS variables
- Sidebar titles, content, and arrows now adapt to theme

static/css/01-foundation/_themes.css

@@ -99,8 +99,8 @@
   --accent-blue: #3399ff;
   --accent-green: #2ecc71;
 
-  /* Sidebar (for non-clean theme) */
-  --sidebar-bg: #2a2a2a;
+  /* Sidebar (for non-clean theme) - darker than light theme but lighter than main content */
+  --sidebar-bg: #3a3d3e;
 
   /* Legacy CV content variables - theme-aware overrides */
   --text-dark: #e0e0e0;  /* Light text for dark background */