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/voices/+server.ts

@@ -1,17 +1,15 @@
 import { json } from '@sveltejs/kit';
 import type { RequestHandler } from './$types';
-import { env } from '$env/dynamic/private';
-
-const SCRAPER_URL = env.SCRAPER_API_URL ?? 'http://localhost:8080';
+import { backendFetch } from '$lib/server/scraper';
 
 /**
  * GET /api/voices
- * Proxies the voice list from the scraper → Kokoro.
+ * Proxies the voice list from the backend → Kokoro.
  * Returns { voices: string[] }
  */
 export const GET: RequestHandler = async () => {
 	try {
-		const res = await fetch(`${SCRAPER_URL}/api/voices`);
+		const res = await backendFetch('/api/voices');
 		if (!res.ok) {
 			return json({ voices: [] });
 		}