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.

test/download/download.test.ts

@@ -36,7 +36,7 @@ let testDir: string;
 beforeAll(async () => {
     await init();
     await sodium.ready;
-    testDir = mkdtempSync(join(tmpdir(), "quack-test-"));
+    testDir = mkdtempSync(join(tmpdir(), "quak-test-"));
 });
 
 afterAll(() => {
@@ -97,7 +97,7 @@ const mockFetchForBody = (body: Uint8Array) => {
 describe("downloadFile", () => {
     it("downloads, decrypts, and writes a single-chunk file", async () => {
         const plaintext = new TextEncoder().encode(
-            "Hello from quack! This is a test photo payload.",
+            "Hello from quak! This is a test photo payload.",
         );
         const key = sodium.crypto_secretstream_xchacha20poly1305_keygen();
         const { header, ciphertext } = encryptFileBody(plaintext, key);