fix: pre-v0.1 review feedback (#14)

* fix(sdk-android): add @JvmOverloads to Uatu.start

Java callers can now invoke start(application) without supplying a
Configuration, matching the Kotlin default-arg ergonomics.

* feat(agent): add protocol_version to HELLO handshake

ProtocolVersion=1 lives on Message and is set by Hello(). Server.Accept
rejects mismatches with a clear error. SDK upgrades that don't change
the wire format keep the same protocol_version; bump on breaking changes.

* test(agent): assert protocol_version in Hello round-trip

* feat(sdk-android): send protocol_version=1 in HELLO

Mirrors agent.ProtocolVersion on the Go side. Bump in lockstep with
the Go constant when the wire format breaks.

* chore(sample-app): pull @uatu/spec from npm next tag

Replaces the file: dep. Copy-paste users can now npm install against
the registry. The release workflow publishes pre-release tags to
npm dist-tag 'next', so the sample tracks the latest rc without
manual version bumps. Lockfile currently resolves to 0.0.1-rc3.

internal/agent/server_test.go

@@ -141,6 +141,28 @@ func TestServer_SnapshotAndRelease(t *testing.T) {
 	wg.Wait()
 }
 
+func TestServer_AcceptRejectsProtocolVersionMismatch(t *testing.T) {
+	server := newLoopbackServer(t)
+
+	go func() {
+		client, err := net.Dial("tcp", server.Addr().String())
+		if err != nil {
+			return
+		}
+		defer client.Close()
+		mismatched := Hello("0.0.1", "android", "com.x")
+		mismatched.ProtocolVersion = ProtocolVersion + 99
+		_ = WriteMessage(client, mismatched)
+	}()
+
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+	_, err := server.Accept(ctx)
+	if err == nil || !strings.Contains(err.Error(), "protocol version mismatch") {
+		t.Fatalf("expected protocol-version-mismatch error, got %v", err)
+	}
+}
+
 func TestServer_AcceptRequiresHello(t *testing.T) {
 	server := newLoopbackServer(t)