feat(bulk-edit): extend BulkDocumentEditLayout with mode="edit"

- New FieldLabelBadge component (additive / replace variants, WCAG AA contrast)
- WhoWhenSection: hideDate prop, editMode prop renders badges next to sender
  and receivers, hides the meta_location field
- DescriptionSection: editMode prop renders badges next to tags and archive
  fields; new bindable archiveBox / archiveFolder inputs only in editMode
- PersonTypeahead: optional badge prop forwards to FieldLabelBadge
- FileSwitcherStrip FileEntry: file is now optional, documentId added so
  edit-mode entries reference an existing document by UUID
- BulkDocumentEditLayout: mode prop branches drop zone / read-only title /
  callout / save handler. Edit save chunks 500 IDs per PATCH, stops on chunk
  failure with retry, marks per-document errors as chips, clears the bulk
  selection store on full success.

Refs #225

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

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

@@ -2,6 +2,7 @@
 import { untrack } from 'svelte';
 import PersonTypeahead from '$lib/components/PersonTypeahead.svelte';
 import PersonMultiSelect from '$lib/components/PersonMultiSelect.svelte';
+import FieldLabelBadge from './FieldLabelBadge.svelte';
 import { isoToGerman, handleGermanDateInput } from '$lib/utils/date';
 import { m } from '$lib/paraglide/messages.js';
 import type { components } from '$lib/generated/api';
@@ -16,7 +17,9 @@ let {
 	initialLocation = '',
 	initialSenderName = '',
 	suggestedDateIso = '',
-	suggestedSenderName = ''
+	suggestedSenderName = '',
+	hideDate = false,
+	editMode = false
 }: {
 	senderId?: string;
 	selectedReceivers?: Person[];
@@ -26,6 +29,8 @@ let {
 	initialSenderName?: string;
 	suggestedDateIso?: string;
 	suggestedSenderName?: string;
+	hideDate?: boolean;
+	editMode?: boolean;
 } = $props();
 
 let dateDisplay = $state(untrack(() => isoToGerman(initialDateIso)));
@@ -56,60 +61,72 @@ $effect(() => {
 	</h2>
 
 	<div class="grid grid-cols-1 gap-5 md:grid-cols-2">
-		<!-- Datum (required — row 1, col 1) -->
-		<div>
-			<label for="documentDate" class="mb-1 block text-sm font-medium text-ink-2"
-				>{m.form_label_date()}*</label
-			>
-			<input
-				id="documentDate"
-				type="text"
-				inputmode="numeric"
-				value={dateDisplay}
-				oninput={handleDateInput}
-				placeholder={m.form_placeholder_date()}
-				maxlength="10"
-				class="block w-full rounded border border-line px-2 py-3 text-sm shadow-sm
-                       {dateInvalid ? 'border-red-400 focus:outline-none focus-visible:ring-2 focus-visible:ring-red-500' : 'focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring'}"
-				aria-describedby={dateInvalid ? 'date-error' : undefined}
-			/>
-			<input type="hidden" name="documentDate" value={dateIso} />
-			{#if dateInvalid}
-				<p id="date-error" class="mt-1 text-xs text-red-600">{m.form_date_error()}</p>
-			{/if}
-		</div>
+		{#if !hideDate}
+			<!-- Datum (required — row 1, col 1) -->
+			<div data-testid="who-when-date">
+				<label for="documentDate" class="mb-1 block text-sm font-medium text-ink-2"
+					>{m.form_label_date()}*</label
+				>
+				<input
+					id="documentDate"
+					type="text"
+					inputmode="numeric"
+					value={dateDisplay}
+					oninput={handleDateInput}
+					placeholder={m.form_placeholder_date()}
+					maxlength="10"
+					class="block w-full rounded border border-line px-2 py-3 text-sm shadow-sm
+                       {dateInvalid
+						? 'border-red-400 focus:outline-none focus-visible:ring-2 focus-visible:ring-red-500'
+						: 'focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring'}"
+					aria-describedby={dateInvalid ? 'date-error' : undefined}
+				/>
+				<input type="hidden" name="documentDate" value={dateIso} />
+				{#if dateInvalid}
+					<p id="date-error" class="mt-1 text-xs text-red-600">{m.form_date_error()}</p>
+				{/if}
+			</div>
+		{/if}
 
-		<!-- Absender (required — row 1, col 2) -->
+		<!-- Absender (required in upload mode — row 1, col 2) -->
 		<div>
 			<PersonTypeahead
 				name="senderId"
 				label={m.form_label_sender()}
-				required={true}
+				required={!editMode}
 				bind:value={senderId}
 				initialName={initialSenderName}
 				suggestedName={suggestedSenderName}
+				badge={editMode ? 'replace' : undefined}
 			/>
 		</div>
 
 		<!-- Empfänger (optional — row 2, col 1) -->
 		<div>
-			<p class="mb-1 block text-sm font-medium text-ink-2">{m.form_label_receivers()}</p>
+			<p class="mb-1 block text-sm font-medium text-ink-2">
+				{m.form_label_receivers()}
+				{#if editMode}<FieldLabelBadge variant="additive" />{/if}
+			</p>
 			<PersonMultiSelect bind:selectedPersons={selectedReceivers} />
 		</div>
 
-		<!-- Ort (optional — row 2, col 2) -->
-		<div>
-			<label for="location" class="mb-1 block text-sm font-medium text-ink-2"
-				>{m.form_label_location()}</label
-			>
-			<input
-				id="location"
-				type="text"
-				name="location"
-				value={initialLocation}
-				placeholder={m.form_placeholder_location()}
-				class="block w-full rounded border border-line px-2 py-3 text-sm shadow-sm focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring"
-			/>
-		</div>
+		{#if !editMode}
+			<!-- Ort (optional — row 2, col 2). Hidden in editMode: meta_location is
+				 NOT bulk-editable per the issue spec; the three editable location
+				 fields live in DescriptionSection. -->
+			<div>
+				<label for="location" class="mb-1 block text-sm font-medium text-ink-2"
+					>{m.form_label_location()}</label
+				>
+				<input
+					id="location"
+					type="text"
+					name="location"
+					value={initialLocation}
+					placeholder={m.form_placeholder_location()}
+					class="block w-full rounded border border-line px-2 py-3 text-sm shadow-sm focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring"
+				/>
+			</div>
+		{/if}
 	</div>
 </div>