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/routes/documents/new/+page.svelte

@@ -6,6 +6,7 @@ import WhoWhenSection from '$lib/components/document/WhoWhenSection.svelte';
 import DescriptionSection from '$lib/components/document/DescriptionSection.svelte';
 import TranscriptionSection from '$lib/components/document/TranscriptionSection.svelte';
 import FileSectionNew from './FileSectionNew.svelte';
+import { type FilenameParseResult } from '$lib/utils/filename';
 
 let { data, form } = $props();
 
@@ -14,6 +15,8 @@ let senderId = $state(untrack(() => data.initialSenderId));
 let selectedReceivers: { id: string; firstName: string; lastName: string }[] = $state(
 	untrack(() => data.initialReceivers)
 );
+
+let parsedSuggestion = $state<FilenameParseResult>({});
 </script>
 
 <div class="mx-auto max-w-4xl px-4 py-8">
@@ -50,10 +53,16 @@ let selectedReceivers: { id: string; firstName: string; lastName: string }[] = $
 			bind:senderId={senderId}
 			bind:selectedReceivers={selectedReceivers}
 			initialSenderName={data.initialSenderName}
+			suggestedDateIso={parsedSuggestion.dateIso ?? ''}
+			suggestedSenderName={parsedSuggestion.personName ?? ''}
+		/>
+		<DescriptionSection
+			bind:tags={tags}
+			titleRequired={true}
+			suggestedTitle={parsedSuggestion.suggestedTitle ?? ''}
 		/>
-		<DescriptionSection bind:tags={tags} titleRequired={true} />
 		<TranscriptionSection />
-		<FileSectionNew />
+		<FileSectionNew onfileParsed={(r) => (parsedSuggestion = r)} />
 
 		<!-- Sticky Save Bar -->
 		<div