thunder-app/thunder — reverse-engineered prompt

Build me an open source mobile app called Thunder for iOS and Android that works as a friendly client for Lemmy and PieFed. I want users to pick an instance, browse All, Local, and Subscribed feeds, open communities, subscribe, favorite, or block them, and read posts and comment threads in either compact or card style.

People should be able to sign in with multiple accounts or continue as a guest, create and edit posts and comments, vote, save, share, reply, see notifications for replies, mentions, and private messages, and view their profile, saved items, posts, and comments. Add search that can find communities, users, posts, and comments, with useful filters and trending communities.

Make the app feel customizable, with light, dark, OLED, system theme, accent colors, font size controls, swipe actions, keyword filters, and settings import and export. Include localization support and basic update notices from GitHub releases. Use Flutter, and look up current Lemmy, PieFed, and Flutter docs if needed.