refactor(document): address review concerns from PR #660

- Restore JavaDoc on DocumentSearchResult.of() and .paged() factory methods
- Remove redundant null guards on @Builder.Default collections in toListItem()
- Map DocumentListItem fields explicitly in DocumentMultiSelect before cast
- Add DocumentListItem required fields to docFactory in spec

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

frontend/src/lib/document/DocumentMultiSelect.svelte.spec.ts

@@ -10,7 +10,19 @@ const docFactory = (id: string, title: string, date = '1880-01-01') => ({
 	title,
 	documentDate: date,
 	originalFilename: `${title}.pdf`,
-	status: 'UPLOADED',
+	receivers: [],
+	tags: [],
+	completionPercentage: 0,
+	contributors: [],
+	matchData: {
+		titleOffsets: [],
+		senderMatched: false,
+		matchedReceiverIds: [],
+		matchedTagIds: [],
+		snippetOffsets: [],
+		summaryOffsets: []
+	},
+	status: 'UPLOADED' as const,
 	metadataComplete: false,
 	scriptType: 'UNKNOWN' as const,
 	createdAt: '2024-01-01T00:00:00',