feat(#68): lead new document form with file upload, all metadata optional

Restructure the "New Document" page so users can save quickly:

- FileSectionNew becomes the first element, redesigned as a prominent
  upload zone with an icon and large click target
- Title field is rendered standalone below the upload zone; it
  auto-populates from the filename (via parseFilename + stripExtension
  fallback) unless the user has already typed something
- All remaining metadata (who/when, description, transcription) moves
  into a collapsible "Weitere Details" section that auto-expands when
  URL prefill data or a form error is present, or when filename parsing
  detects a date/person
- title is no longer required — the form can be saved with only a file
- DescriptionSection gains a `hideTitle` prop for use in this layout
- `form_label_title` translation key no longer carries a hardcoded `*`;
  the asterisk is rendered by the template only when `titleRequired` is
  set (currently only the edit form)
- E2E tests added for all three scenarios from the issue

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

frontend/src/routes/documents/new/FileSectionNew.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
 import { m } from '$lib/paraglide/messages.js';
-import { parseFilename, type FilenameParseResult } from '$lib/utils/filename';
+import { parseFilename, stripExtension, type FilenameParseResult } from '$lib/utils/filename';
 
 let {
 	onfileParsed
@@ -10,29 +10,58 @@ let {
 
 function handleFileChange(e: Event) {
 	const file = (e.target as HTMLInputElement).files?.[0];
-	if (file) onfileParsed?.(parseFilename(file.name));
+	if (!file) return;
+	const parsed = parseFilename(file.name);
+	const result: FilenameParseResult = {
+		...parsed,
+		suggestedTitle: parsed.suggestedTitle ?? stripExtension(file.name)
+	};
+	onfileParsed?.(result);
 }
 </script>
 
-<div class="rounded-sm border border-line bg-surface p-6 shadow-sm">
-	<h2 class="mb-5 text-xs font-bold tracking-widest text-ink-3 uppercase">
-		{m.doc_section_file()}
-	</h2>
+<div class="rounded-sm border border-line bg-surface shadow-sm">
+	<div class="border-b border-line px-6 py-4">
+		<h2 class="text-xs font-bold tracking-widest text-ink-3 uppercase">
+			{m.doc_section_file()}
+		</h2>
+	</div>
 
-	<label for="file-upload" class="mb-1 block text-sm font-medium text-ink-2">
-		{m.doc_file_upload_label()}
-		<span class="font-normal text-ink-3">({m.doc_file_upload_note()})</span>
+	<label
+		for="file-upload"
+		class="flex cursor-pointer flex-col items-center gap-3 px-6 py-10 transition-colors hover:bg-muted/40"
+	>
+		<svg
+			class="h-10 w-10 text-ink-3"
+			fill="none"
+			stroke="currentColor"
+			viewBox="0 0 24 24"
+			aria-hidden="true"
+		>
+			<path
+				stroke-linecap="round"
+				stroke-linejoin="round"
+				stroke-width="1.5"
+				d="M4 16v1a3 3 0 003 3h10a3 3 0 003-3v-1m-4-8l-4-4m0 0L8 8m4-4v12"
+			/>
+		</svg>
+		<span class="text-sm font-medium text-ink-2">
+			{m.doc_file_upload_label()}
+		</span>
+		<span class="text-xs text-ink-3">{m.doc_file_upload_note()}</span>
 	</label>
-	<input
-		id="file-upload"
-		type="file"
-		name="file"
-		onchange={handleFileChange}
-		class="block w-full cursor-pointer text-sm
-               text-ink-2 file:mr-4 file:rounded
-               file:border-0 file:bg-muted
-               file:px-4 file:py-2
-               file:text-sm file:font-semibold
-               file:text-ink hover:file:bg-muted"
-	/>
+	<div class="px-6 pb-6">
+		<input
+			id="file-upload"
+			type="file"
+			name="file"
+			onchange={handleFileChange}
+			class="block w-full cursor-pointer rounded border border-dashed border-line p-2 text-sm
+			       text-ink-2 file:mr-4 file:rounded
+			       file:border-0 file:bg-muted
+			       file:px-4 file:py-2
+			       file:text-sm file:font-semibold
+			       file:text-ink hover:file:bg-muted"
+		/>
+	</div>
 </div>