Rename quack to quak

German for 'quack', matching the Ente (German for 'duck') naming. All
references updated: package name, CLI binary, X-Client-Package header,
test descriptions, temp dir prefixes, README, Makefile docker tag.

src/auth/types.ts

@@ -3,7 +3,7 @@
 export type Base64 = string;
 
 // The blob the server returns alongside the auth token after a successful
-// login. Together with the user's password, this is everything quack needs
+// login. Together with the user's password, this is everything quak needs
 // to derive the master key, secret key, and auth token.
 export interface KeyAttributes {
     kekSalt: Base64;