feat(new-doc): pre-fill date, sender and title from parsed filename

When a file is selected on the new document page, parseFilename runs
on the filename and suggests date, sender name and title via the new
suggestedDateIso / suggestedSenderName / suggestedTitle props. Each
suggestion is applied only while the respective field is still clean
(not dirty), so manual input is never overwritten.

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

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

@@ -1,4 +1,5 @@
 <script lang="ts">
+import { untrack } from 'svelte';
 import TagInput from '$lib/components/TagInput.svelte';
 import { m } from '$lib/paraglide/messages.js';
 
@@ -7,14 +8,26 @@ let {
 	initialTitle = '',
 	initialDocumentLocation = '',
 	initialSummary = '',
-	titleRequired = false
+	titleRequired = false,
+	suggestedTitle = ''
 }: {
 	tags?: string[];
 	initialTitle?: string;
 	initialDocumentLocation?: string;
 	initialSummary?: string;
 	titleRequired?: boolean;
+	suggestedTitle?: string;
 } = $props();
+
+let titleValue = $state(untrack(() => initialTitle));
+let titleDirty = $state(false);
+
+$effect(() => {
+	const suggested = suggestedTitle;
+	if (suggested && !untrack(() => titleDirty)) {
+		titleValue = suggested;
+	}
+});
 </script>
 
 <div class="rounded-sm border border-line bg-surface p-6 shadow-sm">
@@ -33,7 +46,11 @@ let {
 				id="title"
 				type="text"
 				name="title"
-				value={initialTitle}
+				value={titleValue}
+				oninput={(e) => {
+					titleValue = (e.target as HTMLInputElement).value;
+					titleDirty = true;
+				}}
 				required={titleRequired}
 				class="block w-full rounded border border-line p-2 text-sm shadow-sm focus:border-ink focus:ring-ink"
 			/>