Introduce the Kotlin/Compose Android companion app and extend the TMDB
proxy into a combo server that synchronizes the whole library as an
encrypted snapshot, with all three components (Go server, Android,
desktop) sharing one zero-knowledge crypto envelope and JSON schema.
- server: add PostgreSQL-backed /sync/library (GET/PUT) with optimistic
concurrency (revision + 409 on conflict); sync stays disabled unless
DATABASE_URL is set. Add docker-compose with Postgres.
- desktop: add libsodium CryptoEnvelope, LibrarySerializer and SyncClient;
storage-mode and passphrase settings; a "Sync now" toolbar action with
conflict resolution.
- android: Room-backed library with local/cloud storage modes, encrypted
sync client, and settings UI. The proxy server (URL + token) can be
configured as a TMDB proxy even in local-only mode.
Crypto is identical across platforms: Argon2id (libsodium crypto_pwhash,
INTERACTIVE) + XChaCha20-Poly1305 in a versioned "UMTS" envelope, so a
snapshot encrypted on one client decrypts on the other.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
