feat(frontend): add expandable text component for long fields

Adds ExpandableText.svelte which clamps text to 10 lines and shows a
toggle button only when the content actually overflows. Applied to the
summary and transcription fields on the document detail page.

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

frontend/src/lib/components/ExpandableText.svelte

@@ -0,0 +1,33 @@
+<script lang="ts">
+import { m } from '$lib/paraglide/messages.js';
+
+let { text, maxLines = 10 }: { text: string; maxLines?: number } = $props();
+
+let expanded = $state(false);
+let el = $state<HTMLElement | undefined>(undefined);
+let isClamped = $state(false);
+
+$effect(() => {
+	if (el && !expanded) {
+		isClamped = el.scrollHeight > el.clientHeight;
+	}
+});
+</script>
+
+<div>
+	<div
+		bind:this={el}
+		style={!expanded ? `overflow: hidden; display: -webkit-box; -webkit-box-orient: vertical; -webkit-line-clamp: ${maxLines}` : ''}
+		class="rounded border border-brand-sand bg-brand-sand/30 p-5 font-serif text-sm leading-relaxed whitespace-pre-wrap text-brand-navy"
+	>
+		{text}
+	</div>
+	{#if isClamped || expanded}
+		<button
+			onclick={() => (expanded = !expanded)}
+			class="mt-2 font-sans text-xs text-gray-400 transition hover:text-brand-navy"
+		>
+			{expanded ? m.comp_expandable_show_less() : m.comp_expandable_show_more()}
+		</button>
+	{/if}
+</div>