feat: add cardBtn style for card title row buttons

Smaller variant for buttons that sit next to section labels in card headers
(Preview, Color, Results rows). Applied to QRPreview, FontPreview,
ColorManipulation, and FileConverter.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components/color/ColorManipulation.tsx

@@ -10,7 +10,7 @@ import { ExportMenu } from '@/components/color/ExportMenu';
 import { useColorInfo, useGeneratePalette, useGenerateGradient } from '@/lib/color/api/queries';
 import { Loader2, Share2, Plus, X, Palette, Layers } from 'lucide-react';
 import { toast } from 'sonner';
-import { cn, actionBtn } from '@/lib/utils';
+import { cn, actionBtn, cardBtn } from '@/lib/utils';
 import { MobileTabs } from '@/components/ui/mobile-tabs';
 
 type HarmonyType = 'monochromatic' | 'analogous' | 'complementary' | 'triadic' | 'tetradic';
@@ -126,7 +126,7 @@ function ColorManipulationContent() {
               <span className="text-[10px] font-semibold text-muted-foreground uppercase tracking-widest">
                 Color
               </span>
-              <button onClick={handleShare} className={actionBtn}>
+              <button onClick={handleShare} className={cardBtn}>
                 <Share2 className="w-3 h-3" /> Share
               </button>
             </div>