chore: migrate to v3, Doppler secrets, clean up legacy code

- Remove all pre-v3 code: scraper, ui-v2, backend v1, ios v1+v2, legacy CI workflows
- Flatten v3/ contents to repo root
- Add Doppler secrets management (project=libnovel, config=prd)
- Add justfile with doppler run wrappers for all docker compose commands
- Strip hardcoded env fallbacks from docker-compose.yml
- Add minimal README.md
- Clean up .gitignore

ui/src/routes/api/catalogue-page/+server.ts

@@ -0,0 +1,47 @@
+import { json, error } from '@sveltejs/kit';
+import type { RequestHandler } from './$types';
+import { log } from '$lib/server/logger';
+import { backendFetch } from '$lib/server/scraper';
+import { bookToListing, type CatalogueResponse } from '$lib/server/catalogue';
+
+/**
+ * GET /api/catalogue-page?page=2&genre=all&sort=popular&status=all&q=
+ *
+ * Thin proxy to the Go backend's /api/catalogue endpoint.
+ * Used by the infinite-scroll catalogue page to append subsequent pages
+ * without a full SSR navigation.
+ *
+ * Returns { novels, page, hasNext } — the shape expected by the client-side
+ * infinite scroll in +page.svelte.
+ */
+export const GET: RequestHandler = async ({ url }) => {
+	const page = url.searchParams.get('page') ?? '1';
+	const genre = url.searchParams.get('genre') ?? 'all';
+	const sort = url.searchParams.get('sort') ?? 'popular';
+	const status = url.searchParams.get('status') ?? 'all';
+	const q = url.searchParams.get('q') ?? '';
+
+	const params = new URLSearchParams({ page, genre, sort, status });
+	if (q.trim().length >= 2) {
+		params.set('q', q.trim());
+	}
+
+	try {
+		const res = await backendFetch(`/api/catalogue?${params.toString()}`);
+		if (!res.ok) {
+			log.error('catalogue-page', 'backend returned error', { status: res.status });
+			throw error(502, `Catalogue fetch failed: ${res.status}`);
+		}
+		const data: CatalogueResponse = await res.json();
+
+		return json({
+			novels: (data.books ?? []).map(bookToListing),
+			page: data.page ?? (parseInt(page, 10) || 1),
+			hasNext: data.has_next ?? false
+		});
+	} catch (e) {
+		if (e instanceof Error && 'status' in e) throw e;
+		log.error('catalogue-page', 'network error', { err: String(e) });
+		throw error(502, 'Could not reach catalogue service');
+	}
+};