perf: stream slow load functions in admin pages to unblock navigation

- image-gen, text-gen: books list streamed (listBooks is expensive on cold cache)
- ai-jobs: jobs list streamed; add 30s cache to listAIJobs (was uncached listAll)
- changelog: Gitea releases streamed on cold cache; cached path stays synchronous
- admin/+layout.svelte: remove duplicate audio/translation/image-gen nav links

ui/src/routes/admin/text-gen/+page.server.ts

@@ -17,21 +17,23 @@ export interface TextModelInfo {
 }
 
 export const load: PageServerLoad = async () => {
-	// Parent layout already guards admin role.
-	const [models, booksResult] = await Promise.allSettled([
-		listTextModels<TextModelInfo>(),
-		listBooks()
-	]);
+	// Await models immediately — in-memory list, no I/O, returns instantly.
+	// Books are streamed so the page renders at once and the selector
+	// populates a moment later without blocking navigation.
+	const modelsResult = await listTextModels<TextModelInfo>().catch((e) => {
+		log.warn('admin/text-gen', 'failed to load models', { err: String(e) });
+		return [] as TextModelInfo[];
+	});
 
-	if (models.status === 'rejected') {
-		log.warn('admin/text-gen', 'failed to load models', { err: String(models.reason) });
-	}
+	const booksPromise = listBooks()
+		.then((all) =>
+			all.map((b) => ({ slug: b.slug, title: b.title })) as BookSummary[]
+		)
+		.catch(() => [] as BookSummary[]);
 
 	return {
-		models: models.status === 'fulfilled' ? models.value : ([] as TextModelInfo[]),
-		books: (booksResult.status === 'fulfilled' ? booksResult.value : []).map((b) => ({
-			slug: b.slug,
-			title: b.title
-		})) as BookSummary[]
+		models: modelsResult,
+		// Streamed — SvelteKit resolves this after the initial HTML is sent.
+		books: booksPromise
 	};
 };