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/bulkSelection.svelte.spec.ts

@@ -0,0 +1,76 @@
+import { afterEach, describe, expect, it } from 'vitest';
+import { bulkSelectionStore } from './bulkSelection.svelte';
+
+describe('bulkSelectionStore', () => {
+	afterEach(() => bulkSelectionStore.clear());
+
+	it('starts empty', () => {
+		expect(bulkSelectionStore.size).toBe(0);
+	});
+
+	it('toggle adds an id when absent', () => {
+		bulkSelectionStore.toggle('a');
+		expect(bulkSelectionStore.has('a')).toBe(true);
+		expect(bulkSelectionStore.size).toBe(1);
+	});
+
+	it('toggle removes an id when present', () => {
+		bulkSelectionStore.add('a');
+		bulkSelectionStore.toggle('a');
+		expect(bulkSelectionStore.has('a')).toBe(false);
+	});
+
+	it('add and remove update size', () => {
+		bulkSelectionStore.add('a');
+		bulkSelectionStore.add('b');
+		expect(bulkSelectionStore.size).toBe(2);
+		bulkSelectionStore.remove('a');
+		expect(bulkSelectionStore.size).toBe(1);
+		expect(bulkSelectionStore.has('b')).toBe(true);
+	});
+
+	it('add is idempotent', () => {
+		bulkSelectionStore.add('a');
+		bulkSelectionStore.add('a');
+		expect(bulkSelectionStore.size).toBe(1);
+	});
+
+	it('setAll replaces the selection', () => {
+		bulkSelectionStore.add('a');
+		bulkSelectionStore.add('b');
+		bulkSelectionStore.setAll(['c', 'd', 'e']);
+		expect(bulkSelectionStore.size).toBe(3);
+		expect(bulkSelectionStore.has('a')).toBe(false);
+		expect(bulkSelectionStore.has('c')).toBe(true);
+	});
+
+	it('clear empties the selection', () => {
+		bulkSelectionStore.add('a');
+		bulkSelectionStore.add('b');
+		bulkSelectionStore.clear();
+		expect(bulkSelectionStore.size).toBe(0);
+	});
+
+	it('setAll([]) leaves the store empty (no-op when filter returned zero matches)', () => {
+		bulkSelectionStore.add('a');
+		bulkSelectionStore.setAll([]);
+		expect(bulkSelectionStore.size).toBe(0);
+	});
+
+	it('setAll drops all previously selected ids, not just some', () => {
+		bulkSelectionStore.add('a');
+		bulkSelectionStore.add('b');
+		bulkSelectionStore.setAll(['c', 'd']);
+		expect(bulkSelectionStore.has('a')).toBe(false);
+		expect(bulkSelectionStore.has('b')).toBe(false);
+		expect(bulkSelectionStore.has('c')).toBe(true);
+		expect(bulkSelectionStore.has('d')).toBe(true);
+	});
+
+	it('ids getter exposes the current SvelteSet', () => {
+		bulkSelectionStore.add('a');
+		bulkSelectionStore.add('b');
+		const ids = Array.from(bulkSelectionStore.ids);
+		expect(ids.sort()).toEqual(['a', 'b']);
+	});
+});