feat(ui): add structured JSON logging to all server-side routes and lib

Introduces a logger.ts module emitting slog-compatible JSON lines to stderr.
Replaces silent catch blocks and console.error calls throughout minio.ts,
pocketbase.ts, hooks.server.ts, login, books, browse, and all API routes so
auth/registration failures, MinIO presign errors, and scraper proxy failures
are now visible in container logs.

ui/src/routes/api/scrape/+server.ts

@@ -18,6 +18,7 @@
 import { json, error } from '@sveltejs/kit';
 import type { RequestHandler } from './$types';
 import { env } from '$env/dynamic/private';
+import { log } from '$lib/server/logger';
 
 const SCRAPER_URL = env.SCRAPER_API_URL ?? 'http://localhost:8080';
 
@@ -39,11 +40,22 @@ export const POST: RequestHandler = async ({ request, locals }) => {
 	const endpoint = isBookScrape ? '/scrape/book' : '/scrape';
 
 	const upstream = `${SCRAPER_URL}${endpoint}`;
-	const res = await fetch(upstream, {
-		method: 'POST',
-		headers: { 'Content-Type': 'application/json' },
-		body: isBookScrape ? JSON.stringify({ url: body.url }) : undefined
-	});
+	let res: Response;
+	try {
+		res = await fetch(upstream, {
+			method: 'POST',
+			headers: { 'Content-Type': 'application/json' },
+			body: isBookScrape ? JSON.stringify({ url: body.url }) : undefined
+		});
+	} catch (e) {
+		log.error('scrape', 'scraper proxy network error', { endpoint, err: String(e) });
+		throw error(502, 'Could not reach scraper');
+	}
+
+	if (!res.ok && res.status >= 500) {
+		const text = await res.text().catch(() => '');
+		log.error('scrape', 'scraper returned error', { endpoint, status: res.status, body: text });
+	}
 
 	const data = await res.json().catch(() => ({}));