feat: add :backend:api module with interfaces and models (Step 2)

Add the backend API module skeleton with BackendLifecycle interface,
BackendState enum, NoopBackendLifecycle, GatewaySettings, and
GatewaySettingsStore for the dual-flavor architecture.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

android/backend/api/build.gradle.kts

@@ -0,0 +1,21 @@
+plugins {
+    alias(libs.plugins.android.library)
+}
+
+android {
+    namespace = "io.clawdroid.backend.api"
+    compileSdk = libs.versions.android.compileSdk.get().toInt()
+
+    defaultConfig {
+        minSdk = libs.versions.android.minSdk.get().toInt()
+    }
+
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_17
+        targetCompatibility = JavaVersion.VERSION_17
+    }
+}
+
+dependencies {
+    implementation(libs.coroutines.android)
+}

android/backend/api/src/main/AndroidManifest.xml

@@ -0,0 +1,2 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest />

android/backend/api/src/main/java/io/clawdroid/backend/api/BackendLifecycle.kt

@@ -0,0 +1,10 @@
+package io.clawdroid.backend.api
+
+import kotlinx.coroutines.flow.StateFlow
+
+interface BackendLifecycle {
+    val state: StateFlow<BackendState>
+    val isManaged: Boolean
+    suspend fun start()
+    suspend fun stop()
+}

android/backend/api/src/main/java/io/clawdroid/backend/api/BackendState.kt

@@ -0,0 +1,3 @@
+package io.clawdroid.backend.api
+
+enum class BackendState { STOPPED, STARTING, RUNNING, ERROR }

android/backend/api/src/main/java/io/clawdroid/backend/api/GatewaySettings.kt

@@ -0,0 +1,7 @@
+package io.clawdroid.backend.api
+
+data class GatewaySettings(
+    val wsPort: Int = 18793,
+    val httpPort: Int = 18790,
+    val apiKey: String = "",
+)

android/backend/api/src/main/java/io/clawdroid/backend/api/GatewaySettingsStore.kt

@@ -0,0 +1,8 @@
+package io.clawdroid.backend.api
+
+import kotlinx.coroutines.flow.StateFlow
+
+interface GatewaySettingsStore {
+    val settings: StateFlow<GatewaySettings>
+    suspend fun update(settings: GatewaySettings)
+}

android/backend/api/src/main/java/io/clawdroid/backend/api/NoopBackendLifecycle.kt

@@ -0,0 +1,11 @@
+package io.clawdroid.backend.api
+
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+
+class NoopBackendLifecycle : BackendLifecycle {
+    override val state: StateFlow<BackendState> = MutableStateFlow(BackendState.RUNNING)
+    override val isManaged: Boolean = false
+    override suspend fun start() {}
+    override suspend fun stop() {}
+}

android/settings.gradle.kts

@@ -18,3 +18,4 @@ include(":feature:chat")
 include(":core:domain")
 include(":core:data")
 include(":core:ui")
+include(":backend:api")