Add HealthChat API service layer (#1)

* feat(healthchat): add HealthChat API service layer

New features/healthchat modules: typed Retrofit client with
per-request Matrix token auth, member directory, profile and
invite services, plus test fakes and fixtures.

* test(healthchat): use runCatchingExceptions

Detekt's RunCatchingNotAllowed rule forbids plain runCatching.

features/healthchat/impl/build.gradle.kts

@@ -0,0 +1,68 @@
+import extension.buildConfigFieldStr
+import extension.readLocalProperty
+import extension.setupDependencyInjection
+import extension.testCommonDependencies
+
+/*
+ * Copyright (c) 2026 Novaloop AG
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+plugins {
+    id("io.element.android-compose-library")
+    alias(libs.plugins.kotlin.serialization)
+}
+
+android {
+    namespace = "io.element.android.features.healthchat.impl"
+
+    testOptions {
+        unitTests {
+            isIncludeAndroidResources = true
+        }
+    }
+
+    buildFeatures {
+        buildConfig = true
+    }
+
+    defaultConfig {
+        buildConfigFieldStr(
+            name = "HEALTHCHAT_API_BASE_URL",
+            value = System.getenv("HEALTHCHAT_API_BASE_URL")
+                ?: readLocalProperty("healthchat.api.base.url")
+                ?: "https://api.healthchat.ch",
+        )
+    }
+}
+
+setupDependencyInjection()
+
+dependencies {
+    api(projects.features.healthchat.api)
+    implementation(libs.coroutines.core)
+    implementation(platform(libs.network.okhttp.bom))
+    implementation(libs.network.okhttp.okhttp)
+    implementation(libs.network.okhttp.logging)
+    implementation(platform(libs.network.retrofit.bom))
+    implementation(libs.network.retrofit)
+    implementation(libs.network.retrofit.converter.serialization)
+    implementation(libs.serialization.json)
+    implementation(projects.libraries.androidutils)
+    implementation(projects.libraries.architecture)
+    implementation(projects.libraries.core)
+    implementation(projects.libraries.matrix.api)
+    implementation(projects.libraries.network)
+    implementation(projects.libraries.sessionStorage.api)
+
+    testCommonDependencies(libs)
+    testImplementation(libs.network.mockwebserver)
+    testImplementation(projects.features.healthchat.test)
+    testImplementation(projects.libraries.matrix.test)
+    testImplementation(projects.libraries.preferences.api)
+    testImplementation(projects.libraries.preferences.test)
+    testImplementation(projects.libraries.sessionStorage.test)
+}