refactor: move document domain core to lib/document/

Moves ~25 components, utils (search, filename, groupDocuments,
documentStatusLabel, validateFile), bulkSelection store, and
TranscriptionSection sub-component. Fixes broken relative imports.

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

frontend/src/lib/document/BulkDropZone.svelte

@@ -0,0 +1,80 @@
+<script lang="ts">
+import { m } from '$lib/paraglide/messages.js';
+
+let {
+	onFilesAdded
+}: {
+	onFilesAdded: (files: File[]) => void;
+} = $props();
+
+let isDragging = $state(false);
+</script>
+
+<div
+	role="region"
+	aria-label={m.bulk_drop_zone_label()}
+	aria-describedby="bulk-drop-desc"
+	data-testid="bulk-drop-zone"
+	class="flex flex-1 flex-col items-center justify-center p-6"
+	ondragover={(e) => {
+		e.preventDefault();
+		isDragging = true;
+	}}
+	ondragleave={() => (isDragging = false)}
+	ondrop={(e) => {
+		e.preventDefault();
+		isDragging = false;
+		if (e.dataTransfer && e.dataTransfer.files.length > 0) {
+			onFilesAdded(Array.from(e.dataTransfer.files));
+		}
+	}}
+>
+	<div
+		class={[
+			'flex w-full max-w-xl flex-col items-center gap-5 rounded-md border-2 border-dashed px-12 py-16 text-center transition-colors',
+			isDragging ? 'border-accent bg-accent/10' : 'border-accent/50 bg-white/[0.04]'
+		].join(' ')}
+	>
+		<!-- Circular mint icon -->
+		<div class="flex h-20 w-20 items-center justify-center rounded-full bg-accent text-primary">
+			<svg
+				width="32"
+				height="32"
+				viewBox="0 0 32 32"
+				xmlns="http://www.w3.org/2000/svg"
+				aria-hidden="true"
+			>
+				<polygon
+					fill="currentColor"
+					points="6 12.5 16 2 26 12.5 24.5714286 14 16.999 6.049 17 30 15 30 14.999 6.051 7.42857143 14"
+				/>
+			</svg>
+		</div>
+
+		<!-- Serif title -->
+		<p class="font-serif text-base font-bold text-ink">{m.bulk_drop_hint()}</p>
+
+		<!-- Sub description -->
+		<p id="bulk-drop-desc" class="text-sm leading-relaxed text-ink-2">{m.bulk_drop_desc()}</p>
+
+		<!-- CTA button -->
+		<label
+			class="flex min-h-[44px] cursor-pointer items-center rounded-sm bg-primary px-6 py-2 text-xs font-bold tracking-widest text-primary-fg uppercase transition-opacity hover:opacity-90"
+		>
+			{m.bulk_select_files()}
+			<input
+				type="file"
+				multiple
+				accept="application/pdf"
+				class="sr-only"
+				onchange={(e) => {
+					const files = Array.from(e.currentTarget.files ?? []);
+					if (files.length > 0) onFilesAdded(files);
+				}}
+			/>
+		</label>
+
+		<!-- Format hint -->
+		<p class="text-xs text-ink-3">{m.bulk_drop_sub()}</p>
+	</div>
+</div>