refactor(kmp/ed25519): rename modules + mnemonic Kotlin rewrite

- Rename :libs:encryption:ed25519-kmp → :libs:encryption:ed25519
  (KMP module takes the clean name; no -kmp suffix exposed to consumers)
- Rename :libs:encryption:ed25519 → :libs:encryption:ed25519-native
  (JNI/CMake module becomes an internal impl detail; androidMain delegates to it)
- Update cinterop path in ed25519.def and C source reference in build.gradle.kts
- Update kmpUnitTestModules and settings.gradle.kts registrations
- Update :kmp:shared-core api/export references
- Convert MnemonicCode and MnemonicException from Java to Kotlin
  (cherry-picked from origin/fix/kmp-consumer-compile)

Author: bmc08gt

kmp/shared-core/build.gradle.kts

@@ -24,7 +24,7 @@ kotlin {
             export(project(":libs:encryption:sha256"))
             export(project(":libs:encryption:sha512"))
             export(project(":libs:encryption:hmac"))
-            export(project(":libs:encryption:ed25519-kmp"))
+            export(project(":libs:encryption:ed25519"))
         }
     }
 
@@ -35,7 +35,7 @@ kotlin {
                 api(project(":libs:encryption:sha256"))
                 api(project(":libs:encryption:sha512"))
                 api(project(":libs:encryption:hmac"))
-                api(project(":libs:encryption:ed25519-kmp"))
+                api(project(":libs:encryption:ed25519"))
             }
         }
     }

libs/encryption/ed25519-kmp/build.gradle.kts

@@ -0,0 +1,30 @@
+plugins {
+    alias(libs.plugins.flipcash.android.library)
+}
+
+android {
+    namespace = "${Gradle.codeNamespace}.ed25519"
+    ndkVersion = "29.0.14206865"
+    defaultConfig {
+        externalNativeBuild {
+            cmake {
+                cppFlags += "-std=c++11"
+            }
+        }
+    }
+
+    externalNativeBuild {
+        cmake {
+            path = file("CMakeLists.txt")
+        }
+    }
+}
+
+dependencies {
+    implementation(fileTree(mapOf("dir" to "libs", "include" to listOf("*.jar"))))
+    implementation(libs.bundles.kotlinx.serialization)
+
+    // Cross-platform test-vector gate (instrumented: JNI + android.util.Base64 need a device).
+    androidTestImplementation(libs.androidx.junit)
+    androidTestImplementation(libs.androidx.test.runner)
+}