tabs: more configurable content padding options

choice between margin and padding. ngl, this feels kind of dumb, it
wasn't be problem and I don't know when it would ever be a problem.
perhaps i'll simplify or revert this later.

src/lib/Tabs.svelte

@@ -26,7 +26,7 @@
 		/** Applies layout padding to the tab header (default: false) */
 		padHeader?: boolean;
 		/** Applies layout padding to the content areas (default: false) */
-		padContent?: boolean;
+		padContent?: 'padding' | 'margin' | 'none';
 		/** Additional classes applied to the outer container */
 		class?: ClassValue | null;
 	}
@@ -36,7 +36,7 @@
 		activeIndex = 0,
 		onchange,
 		padHeader = false,
-		padContent = false,
+		padContent = 'none',
 		class: classValue
 	}: Props = $props();
 
@@ -144,7 +144,7 @@
 
 	{#key activeIndex}
 		<div
-			class={[padContent && 'px-layout']}
+			class={[padContent === 'padding' && 'px-layout', padContent === 'margin' && 'mx-layout']}
 			in:flyX={{ direction: activeIndex > prevIndex ? 1 : -1, duration: 180, delay: 181 }}
 			out:flyX={{ direction: activeIndex > prevIndex ? -1 : 1, duration: 180 }}
 			onoutrostart={lockHeight}