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/client.ts

@@ -86,7 +86,7 @@ export class Client {
             const code = await opts.emailOTP();
             response = await submitEmailOTP(api, opts.email, code);
         } else if (challenge.kind === "passkey") {
-            throw new Error("Passkey authentication is not supported by quack");
+            throw new Error("Passkey authentication is not supported by quak");
         } else {
             throw new Error(`Unknown login challenge kind`);
         }