feat(bulk-upload): add BulkDocumentEditLayout component with save handler

State-owner for the bulk upload flow:
- N=0: full-panel BulkDropZone
- N=1: title + shared metadata (no switcher/scope cards)
- N≥2: FileSwitcherStrip + per-file ScopeCard + shared ScopeCard
Save handler chunks files at 10/request, POSTs to /api/documents/quick-upload
with typed metadata JSON part, tracks progress, redirects to /documents.

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

frontend/src/lib/components/document/UploadSaveBar.svelte

@@ -30,6 +30,7 @@ let {
 		</button>
 		<button
 			type="button"
+			data-testid="bulk-save-btn"
 			onclick={onSave}
 			class="min-h-[44px] rounded-sm bg-brand-navy px-6 text-sm font-bold tracking-widest text-white uppercase hover:bg-brand-navy/90"
 		>