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/transcription/TranscriptionSection.svelte

@@ -0,0 +1,19 @@
+<script lang="ts">
+import { m } from '$lib/paraglide/messages.js';
+
+let { initialTranscription = '' }: { initialTranscription?: string } = $props();
+</script>
+
+<div class="rounded-sm border border-line bg-surface p-6 shadow-sm">
+	<h2 class="mb-5 text-xs font-bold tracking-widest text-ink-3 uppercase">
+		{m.form_label_transcription()}
+	</h2>
+	<textarea
+		id="transcription"
+		name="transcription"
+		rows="12"
+		placeholder={m.form_placeholder_transcription()}
+		class="block w-full rounded border border-line p-2 font-serif text-sm shadow-sm focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring"
+		>{initialTranscription}</textarea
+	>
+</div>