refine: improve UI consistency and spacing in header and provider cards

- Reduce header spacing (gap-4 → gap-2, gap-1.5 → gap-1) for more compact layout
- Unify provider link colors with main title (blue-500/blue-400)
- Standardize action button styles to use size="icon" for consistent hover effects
- Add proper hover backgrounds to provider action buttons matching header buttons

src/components/providers/ProviderCard.tsx

@@ -132,7 +132,7 @@ export function ProviderCard({
               <button
                 type="button"
                 onClick={handleOpenWebsite}
-                className="inline-flex items-center text-sm text-blue-400 transition-colors hover:underline dark:text-blue-300"
+                className="inline-flex items-center text-sm text-blue-500 transition-colors hover:underline dark:text-blue-400"
                 title={displayUrl}
               >
                 <span className="truncate">{displayUrl}</span>