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/api/build.gradle.kts

@@ -0,0 +1,22 @@
+/*
+ * 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")
+}
+
+android {
+    namespace = "io.element.android.features.healthchat.api"
+}
+
+dependencies {
+    api(libs.kotlinx.collections.immutable)
+    implementation(libs.coroutines.core)
+    implementation(projects.libraries.architecture)
+    implementation(projects.libraries.designsystem)
+    api(projects.libraries.matrix.api)
+}