feat: integrate Tauri v2 with Android widget and voice assistant

- Add Tauri v2 shell (Cargo, tauri.conf.json, capabilities, plugins)
- Migrate all fetch() calls to apiFetch() for Tauri-aware HTTP
- Migrate WebSocket endpoints to resolveEndpoints() for dynamic URLs
- Add ServerConfigDialog for remote server URL configuration
- Add tauri.ts lib with isTauri detection, apiFetch wrapper, plugin helpers
- Add server-config Pinia store with persistence via plugin-store
- Conditional PWA (disabled in Tauri builds)
- Android: home screen transcript widget (last 5 messages, 30s refresh)
- Android: voice command / share activity (SpeechRecognizer + WebSocket)
- Android: signed release APK with auto-copy to installers/
- Remove stale frontend/src-tauri directory

src-tauri/gen/android/app/build.gradle.kts

@@ -0,0 +1,97 @@
+import java.util.Properties
+
+plugins {
+    id("com.android.application")
+    id("org.jetbrains.kotlin.android")
+    id("rust")
+}
+
+val tauriProperties = Properties().apply {
+    val propFile = file("tauri.properties")
+    if (propFile.exists()) {
+        propFile.inputStream().use { load(it) }
+    }
+}
+
+android {
+    signingConfigs {
+        create("release") {
+            storeFile = file("../keystore.jks")
+            storePassword = "agentui123"
+            keyAlias = "agentui"
+            keyPassword = "agentui123"
+        }
+    }
+    compileSdk = 36
+    namespace = "com.agentui.desktop"
+    defaultConfig {
+        manifestPlaceholders["usesCleartextTraffic"] = "false"
+        applicationId = "com.agentui.desktop"
+        minSdk = 24
+        targetSdk = 36
+        versionCode = tauriProperties.getProperty("tauri.android.versionCode", "1").toInt()
+        versionName = tauriProperties.getProperty("tauri.android.versionName", "1.0")
+    }
+    buildTypes {
+        getByName("debug") {
+            manifestPlaceholders["usesCleartextTraffic"] = "true"
+            isDebuggable = true
+            isJniDebuggable = true
+            isMinifyEnabled = false
+            packaging {                jniLibs.keepDebugSymbols.add("*/arm64-v8a/*.so")
+                jniLibs.keepDebugSymbols.add("*/armeabi-v7a/*.so")
+                jniLibs.keepDebugSymbols.add("*/x86/*.so")
+                jniLibs.keepDebugSymbols.add("*/x86_64/*.so")
+            }
+        }
+        getByName("release") {
+            signingConfig = signingConfigs.getByName("release")
+            isMinifyEnabled = true
+            proguardFiles(
+                *fileTree(".") { include("**/*.pro") }
+                    .plus(getDefaultProguardFile("proguard-android-optimize.txt"))
+                    .toList().toTypedArray()
+            )
+        }
+    }
+    kotlinOptions {
+        jvmTarget = "1.8"
+    }
+    buildFeatures {
+        buildConfig = true
+    }
+}
+
+rust {
+    rootDirRel = "../../../../"
+}
+
+dependencies {
+    implementation("androidx.webkit:webkit:1.14.0")
+    implementation("androidx.appcompat:appcompat:1.7.1")
+    implementation("androidx.activity:activity-ktx:1.10.1")
+    implementation("com.google.android.material:material:1.12.0")
+    implementation("androidx.work:work-runtime-ktx:2.9.0")
+    implementation("com.squareup.okhttp3:okhttp:4.12.0")
+    testImplementation("junit:junit:4.13.2")
+    androidTestImplementation("androidx.test.ext:junit:1.1.4")
+    androidTestImplementation("androidx.test.espresso:espresso-core:3.5.0")
+}
+
+apply(from = "tauri.build.gradle.kts")
+
+// Copy APK to src-tauri/installers after build
+android.applicationVariants.all {
+    val variant = this
+    variant.outputs.all {
+        val output = this
+        variant.assembleProvider.get().doLast {
+            val src = output.outputFile
+            if (src.exists()) {
+                val dest = file("../../../../installers/AgentUI-${variant.versionName}-${variant.name}.apk")
+                src.copyTo(dest, overwrite = true)
+                println(">> Copied APK to ${dest.absolutePath}")
+            }
+        }
+    }
+}