fix(watch): corrige l'URL serveur et ajoute les tests associes (#186)

Aligne http_api_client.dart avec la config watch (build.gradle.kts,
WatchHeartRateCollector) et couvre le comportement par des tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

watch_app/android/app/build.gradle.kts

@@ -80,4 +80,6 @@ dependencies {
     implementation("androidx.wear:wear-ongoing:1.0.0")
     implementation("com.google.guava:guava:33.6.0-android")
     implementation("com.google.android.gms:play-services-wearable:19.0.0")
+
+    testImplementation(kotlin("test"))
 }