feat(sdk): add Java and Ruby SDK wrappers over C FFI

Java SDK: JNI bindings to libquicproquo_ffi with QpqClient class,
Gradle build, and exception hierarchy matching Kotlin SDK.

Ruby SDK: FFI gem wrapping libquicproquo_ffi with Client class,
block-form auto-disconnect, gemspec for RubyGems publishing,
and example script.

sdks/java/build.gradle.kts

@@ -0,0 +1,24 @@
+plugins {
+    java
+}
+
+group = "dev.quicproquo"
+version = "0.1.0"
+
+java {
+    sourceCompatibility = JavaVersion.VERSION_17
+    targetCompatibility = JavaVersion.VERSION_17
+}
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    implementation("com.google.code.gson:gson:2.10.1")
+    testImplementation("org.junit.jupiter:junit-jupiter:5.10.2")
+}
+
+tasks.test {
+    useJUnitPlatform()
+}