Client.login(email, password) performs the full SRP handshake, key
unwrap, and returns a ready Client. Session lives in the object.
Client.fromJSON(snapshot) restores from a serialized snapshot.
client.toJSON() produces a plain object with base64-encoded keys
that the consumer can persist however they like.
Methods: whoami, listCollections, listFiles (with pagination),
downloadFile, downloadThumbnail, logout.
All 86 tests pass including the 8-part literate usage tutorial.
test/client/usage.test.ts is a tutorial-as-test-suite that walks
through the entire quack API in order: login, whoami, listCollections,
listFiles, downloadFile, downloadThumbnail, toJSON/fromJSON, logout.
Each it() block is a self-contained example with prose commentary
explaining what the code does and why, with code samples showing the
API as a consumer would use it. The mock server performs real SRP and
crypto so the test data is structurally identical to production.
8 tests, all failing against the stub.
