fix(bulk-edit): drop dead initial-* props and clear store on edit-mode discard

Felix B1 — `WhoWhenSection.svelte:37` and `DescriptionSection.svelte:42`
mutated $bindable props at top-level script scope, seeding them from
`initial*` companion props that no caller ever passes. The pattern stomps
parent-owned state in any future component re-evaluation.

Removed the dead initialDateIso / initialLocation / initialDocumentLocation
props and let the bindables carry their own initial value. dateDisplay and
currentTitle now seed from the bindable directly inside untrack — no
re-assignment required.

Elicit B2 — In edit mode the file map IS the user's bulk selection, so
discarding must clear bulkSelectionStore and bounce back to /documents,
otherwise the user is left on /documents/bulk-edit with an empty form
and a stale count in the bottom bar.

Refs #225, PR #331

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

frontend/src/lib/components/document/BulkDocumentEditLayout.svelte.spec.ts

@@ -315,6 +315,30 @@ describe('BulkDocumentEditLayout', () => {
 
 // ─── mode="edit" ─────────────────────────────────────────────────────────────
 
+describe('BulkDocumentEditLayout — mode="edit" discard', () => {
+	it('discard in edit mode clears the selection store and navigates back to /documents', async () => {
+		const { bulkSelectionStore } = await import('$lib/stores/bulkSelection.svelte');
+		bulkSelectionStore.setAll(['doc-1']);
+
+		const { container } = render(BulkDocumentEditLayout, {
+			mode: 'edit',
+			initialEditEntries: [
+				{ id: 'doc-1', title: 'Brief 1', pdfUrl: '/api/documents/doc-1/file' },
+				{ id: 'doc-2', title: 'Brief 2', pdfUrl: '/api/documents/doc-2/file' }
+			]
+		});
+
+		const discardBtn = container.querySelector(
+			'button[data-testid="discard-all-btn"]'
+		) as HTMLButtonElement;
+		expect(discardBtn).not.toBeNull();
+		discardBtn.click();
+
+		await vi.waitFor(() => expect(goto).toHaveBeenCalledWith('/documents'), { timeout: 1000 });
+		expect(bulkSelectionStore.size).toBe(0);
+	});
+});
+
 describe('BulkDocumentEditLayout — mode="edit"', () => {
 	const editEntry = (i: number) => ({
 		id: `doc-${i}`,