feat(upload): add drag-and-drop bulk upload zone to home page

Adds a compact, unobtrusive drop zone between the search card and the
document list. Only visible to users with WRITE_ALL permission.

- Drag-and-drop or click-to-select multiple files at once
- Client-side MIME type validation with per-file error messages
- POSTs to /api/documents/quick-upload; refreshes list via invalidateAll()
- Inline feedback: success count + per-file errors
- i18n keys added to de/en/es message files

Closes #66 (frontend part)

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

frontend/messages/de.json

@@ -265,5 +265,10 @@
 	"doc_panel_annotation_thread_title": "Annotation",
 	"doc_panel_discussion_annotation_tab": "Annotation · Seite {page}",
 	"pdf_annotations_show": "Annotierungen anzeigen",
-	"pdf_annotations_hide": "Annotierungen verbergen"
+	"pdf_annotations_hide": "Annotierungen verbergen",
+	"upload_drop_hint": "Dateien ablegen oder auswählen",
+	"upload_accepted_types": "PDF, JPEG, PNG, TIFF",
+	"upload_success": "{count} Dokument(e) erstellt",
+	"upload_invalid_type": "{filename}: Dateiformat nicht unterstützt",
+	"upload_error": "Fehler beim Hochladen von {filename}"
 }

frontend/messages/en.json

@@ -265,5 +265,10 @@
 	"doc_panel_annotation_thread_title": "Annotation",
 	"doc_panel_discussion_annotation_tab": "Annotation · Page {page}",
 	"pdf_annotations_show": "Show annotations",
-	"pdf_annotations_hide": "Hide annotations"
+	"pdf_annotations_hide": "Hide annotations",
+	"upload_drop_hint": "Drop files or click to select",
+	"upload_accepted_types": "PDF, JPEG, PNG, TIFF",
+	"upload_success": "{count} document(s) created",
+	"upload_invalid_type": "{filename}: unsupported file format",
+	"upload_error": "Error uploading {filename}"
 }

frontend/messages/es.json

@@ -265,5 +265,10 @@
 	"doc_panel_annotation_thread_title": "Anotación",
 	"doc_panel_discussion_annotation_tab": "Anotación · Página {page}",
 	"pdf_annotations_show": "Mostrar anotaciones",
-	"pdf_annotations_hide": "Ocultar anotaciones"
+	"pdf_annotations_hide": "Ocultar anotaciones",
+	"upload_drop_hint": "Soltar archivos o hacer clic para seleccionar",
+	"upload_accepted_types": "PDF, JPEG, PNG, TIFF",
+	"upload_success": "{count} documento(s) creado(s)",
+	"upload_invalid_type": "{filename}: formato de archivo no admitido",
+	"upload_error": "Error al subir {filename}"
 }

frontend/src/routes/+page.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
 import PersonTypeahead from '$lib/components/PersonTypeahead.svelte';
-import { goto } from '$app/navigation';
+import { goto, invalidateAll } from '$app/navigation';
 import TagInput from '$lib/components/TagInput.svelte';
 import { slide } from 'svelte/transition';
 import { untrack } from 'svelte';
@@ -18,6 +18,13 @@ let senderId = $state(untrack(() => data.filters?.senderId || ''));
 let receiverId = $state(untrack(() => data.filters?.receiverId || ''));
 let tagNames = $state<string[]>(untrack(() => data.filters?.tags || []));
 
+const ACCEPTED_TYPES = ['application/pdf', 'image/jpeg', 'image/png', 'image/tiff'];
+
+let isDragging = $state(false);
+let isUploading = $state(false);
+let uploadMessages = $state<{ text: string; isError: boolean }[]>([]);
+let fileInput: HTMLInputElement;
+
 let searchTimer: ReturnType<typeof setTimeout>;
 
 const hasAdvancedFilters = (filters: typeof data.filters) =>
@@ -29,6 +36,81 @@ const hasAdvancedFilters = (filters: typeof data.filters) =>
 
 let showAdvanced = $state(untrack(() => hasAdvancedFilters(data.filters)));
 
+function handleDragOver(e: DragEvent) {
+	e.preventDefault();
+	isDragging = true;
+}
+
+function handleDragLeave() {
+	isDragging = false;
+}
+
+async function handleDrop(e: DragEvent) {
+	e.preventDefault();
+	isDragging = false;
+	const files = Array.from(e.dataTransfer?.files ?? []);
+	await uploadFiles(files);
+}
+
+async function handleFileSelect(e: Event) {
+	const input = e.target as HTMLInputElement;
+	const files = Array.from(input.files ?? []);
+	input.value = '';
+	await uploadFiles(files);
+}
+
+async function uploadFiles(files: File[]) {
+	if (files.length === 0) return;
+
+	const messages: { text: string; isError: boolean }[] = [];
+
+	// Client-side type validation
+	const valid: File[] = [];
+	for (const file of files) {
+		if (!ACCEPTED_TYPES.includes(file.type)) {
+			messages.push({ text: m.upload_invalid_type({ filename: file.name }), isError: true });
+		} else {
+			valid.push(file);
+		}
+	}
+
+	if (valid.length === 0) {
+		uploadMessages = messages;
+		return;
+	}
+
+	isUploading = true;
+	try {
+		const formData = new FormData();
+		for (const file of valid) {
+			formData.append('files', file);
+		}
+
+		const res = await fetch('/api/documents/quick-upload', {
+			method: 'POST',
+			body: formData
+		});
+
+		if (res.ok) {
+			const result = await res.json();
+			if (result.created?.length > 0) {
+				messages.push({ text: m.upload_success({ count: result.created.length }), isError: false });
+			}
+			for (const err of result.errors ?? []) {
+				messages.push({ text: err, isError: true });
+			}
+			await invalidateAll();
+		} else {
+			for (const file of valid) {
+				messages.push({ text: m.upload_error({ filename: file.name }), isError: true });
+			}
+		}
+	} finally {
+		isUploading = false;
+		uploadMessages = messages;
+	}
+}
+
 function triggerSearch() {
 	const params = new SvelteURLSearchParams();
 
@@ -210,6 +292,43 @@ $effect(() => {
 		{/if}
 	</div>
 
+	{#if data.canWrite}
+		<!-- UPLOAD DROP ZONE -->
+		<div
+			role="button"
+			tabindex="0"
+			class="mb-4 flex cursor-pointer items-center justify-center gap-3 border border-dashed px-6 py-3 text-sm transition-colors duration-150 {isDragging
+				? 'border-accent bg-accent/5 text-accent'
+				: 'border-line-2 text-ink-3 hover:border-accent hover:text-accent'}"
+			ondragover={handleDragOver}
+			ondragleave={handleDragLeave}
+			ondrop={handleDrop}
+			onclick={() => fileInput.click()}
+			onkeydown={(e) => e.key === 'Enter' && fileInput.click()}
+		>
+			<img
+				src="/degruyter-icons/Simple/Medium-24px/SVG/Action/Upload/Upload-MD.svg"
+				alt=""
+				aria-hidden="true"
+				class="h-4 w-4 shrink-0 opacity-50"
+			/>
+			<span class="font-sans font-medium">
+				{isUploading ? '…' : m.upload_drop_hint()}
+			</span>
+			<span class="font-sans text-xs text-ink-3">{m.upload_accepted_types()}</span>
+		</div>
+
+		{#if uploadMessages.length > 0}
+			<div class="mb-4 flex flex-col gap-1">
+				{#each uploadMessages as msg, i (i)}
+					<p class="font-sans text-sm {msg.isError ? 'text-red-600' : 'text-green-700'}">
+						{msg.text}
+					</p>
+				{/each}
+			</div>
+		{/if}
+	{/if}
+
 	<!-- DOCUMENT LIST HEADER -->
 	<div class="mb-2 flex justify-end">
 		{#if data.canWrite}
@@ -360,4 +479,12 @@ $effect(() => {
 			</div>
 		{/if}
 	</div>
+	<input
+		bind:this={fileInput}
+		type="file"
+		multiple
+		accept=".pdf,.jpg,.jpeg,.png,.tif,.tiff"
+		class="sr-only"
+		onchange={handleFileSelect}
+	/>
 </main>