refactor(dashboard): extract settled<T>() helper; fix page.svelte.spec.ts types

Collapses 5x duplicated null-check pattern in the reader fetch branch into
a single typed helper — addresses @Felix review blocker.

Also adds isReader/incompleteDocs/incompleteTotal to page.svelte.spec.ts
baseData so it satisfies the discriminated PageData union introduced by this PR.

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

frontend/src/routes/page.svelte.spec.ts

@@ -20,6 +20,7 @@ const baseData = {
 		enabled: true,
 		createdAt: '2024-01-01T00:00:00Z'
 	} as User,
+	isReader: false as const,
 	canWrite: true,
 	canAnnotate: false,
 	canBlogWrite: false,
@@ -31,6 +32,8 @@ const baseData = {
 	transcriptionDocs: [],
 	readyDocs: [],
 	weeklyStats: null,
+	incompleteDocs: [],
+	incompleteTotal: 0,
 	error: null
 };