Add dynamic sidebar text color with brand color contrast

- Add sidebar text color picker to Branding Settings page
- Implement auto-calculated complementary text colors based on brand color luminance
- Dark themes get light tinted text, light themes get dark tinted text
- Add navigation preview showing text on gradient background
- Support 10 new lighter color palettes (Soft Mint, Lavender, Peach, etc.)
- Add CSS utility classes for brand-text with opacity support
- Update sidebar and navigation components to use dynamic text colors
- Add sidebar_text_color field to Tenant model with migration

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/src/layouts/BusinessLayout.tsx

@@ -66,17 +66,19 @@ const BusinessLayoutContent: React.FC<BusinessLayoutProps> = ({ business, user,
     setTicketModalId(null);
   };
 
-  // Set CSS custom properties for brand colors (primary palette + secondary color)
+  // Set CSS custom properties for brand colors (primary palette + secondary color + sidebar text)
   useEffect(() => {
     applyBrandColors(
       business.primaryColor || '#2563eb',
-      business.secondaryColor || business.primaryColor || '#2563eb'
+      business.secondaryColor || business.primaryColor || '#2563eb',
+      business.sidebarTextColor // Optional custom sidebar text color
     );
 
     // Cleanup: reset to defaults when component unmounts
     return () => {
       applyColorPalette(defaultColorPalette);
       document.documentElement.style.setProperty('--color-brand-secondary', '#0ea5e9');
+      document.documentElement.style.setProperty('--color-brand-text-rgb', '255 255 255');
     };
   }, [business.primaryColor, business.secondaryColor]);