feat: add LinkPopover component for checklist hyperlinks

src/lib/components/LinkPopover.svelte

@@ -0,0 +1,73 @@
+<script lang="ts">
+	import ExternalLink from 'lucide-svelte/icons/external-link';
+	import { onMount } from 'svelte';
+
+	interface Props {
+		url: string;
+		anchor: DOMRect;
+		onClose: () => void;
+	}
+
+	let { url, anchor, onClose }: Props = $props();
+
+	let popoverEl: HTMLDivElement | undefined = $state();
+	let top = $state(0);
+	let left = $state(0);
+
+	onMount(() => {
+		if (!popoverEl) return;
+		const rect = popoverEl.getBoundingClientRect();
+
+		// Position below the anchor link, or above if near viewport bottom
+		const spaceBelow = window.innerHeight - anchor.bottom;
+		if (spaceBelow >= rect.height + 8) {
+			top = anchor.bottom + 4;
+		} else {
+			top = anchor.top - rect.height - 4;
+		}
+
+		left = anchor.left;
+		// Clamp to viewport
+		if (left + rect.width > window.innerWidth - 8) {
+			left = window.innerWidth - rect.width - 8;
+		}
+		if (left < 8) left = 8;
+	});
+
+	function handleClickOutside(e: MouseEvent) {
+		if (popoverEl && !popoverEl.contains(e.target as Node)) {
+			onClose();
+		}
+	}
+
+	function handleKeydown(e: KeyboardEvent) {
+		if (e.key === 'Escape') {
+			onClose();
+		}
+	}
+
+	function openLink() {
+		window.open(url, '_blank', 'noopener');
+		onClose();
+	}
+</script>
+
+<svelte:window onclick={handleClickOutside} onkeydown={handleKeydown} />
+
+<!-- svelte-ignore a11y_no_static_element_interactions -->
+<div
+	bind:this={popoverEl}
+	class="fixed z-50 flex items-center gap-1.5 rounded-sm border border-[var(--border-subtle)] bg-[var(--bg-surface)] px-2 py-1.5 shadow-[var(--card-shadow)]"
+	style="top: {top}px; left: {left}px;"
+	onclick={(e) => e.stopPropagation()}
+	data-testid="link-popover"
+>
+	<button
+		onclick={openLink}
+		class="flex items-center gap-1 text-xs text-[var(--primary)] hover:text-[var(--primary-hover)]"
+		data-testid="link-popover-open"
+	>
+		<ExternalLink class="h-3.5 w-3.5" />
+		Open
+	</button>
+</div>