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/protocol_test.go

@@ -28,6 +28,9 @@ func TestRoundTrip_Hello(t *testing.T) {
 	if got.Type != MessageTypeHello || got.Version != "0.0.1" || got.Platform != "android" || got.AppPackage != "in.okcredit.merchant" {
 		t.Fatalf("hello round-trip failed: %+v", got)
 	}
+	if got.ProtocolVersion != ProtocolVersion {
+		t.Errorf("protocol_version: got %d, want %d", got.ProtocolVersion, ProtocolVersion)
+	}
 }
 
 func TestRoundTrip_PauseResume(t *testing.T) {