fix(watch): corrige applicationId et nettoie la config de build montre

Répare la régression de packaging introduite par le reset/remerge de
develop : l'APK montre était packagée avec com.gametime.app au lieu de
com.gametime.watch (namespace correct mais applicationId hérité du
téléphone), ce qui cassait la détection du bridge. Aligne applicationId
sur com.gametime.watch, nettoie la config de signing partagée sur les
deux modules android/app et watch_app/android/app, et ajuste
use_cases + watch_session_screen en conséquence.

Validé : APK montre release package = com.gametime.watch, même SHA-256
de certificat sur les deux APKs (70cc69e8...45c7815), tests use_cases et
watch_session_screen OK.

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

android/app/build.gradle.kts

@@ -1,3 +1,5 @@
+import java.util.Properties
+
 plugins {
     id("com.android.application")
     id("org.jetbrains.kotlin.android")
@@ -5,6 +7,26 @@ plugins {
     id("dev.flutter.flutter-gradle-plugin")
 }
 
+val sharedSigningPropertiesFile = rootProject.file("key.properties")
+val sharedSigningProperties =
+    Properties().also { properties ->
+        check(sharedSigningPropertiesFile.isFile) {
+            "Shared signing config missing: ${sharedSigningPropertiesFile.absolutePath}"
+        }
+        sharedSigningPropertiesFile.inputStream().use(properties::load)
+    }
+
+fun requiredSharedSigningProperty(name: String): String =
+    sharedSigningProperties.getProperty(name)?.takeIf { it.isNotBlank() }
+        ?: error("Shared signing property '$name' missing in ${sharedSigningPropertiesFile.absolutePath}")
+
+val sharedSigningStoreFile =
+    sharedSigningPropertiesFile.parentFile.resolve(requiredSharedSigningProperty("storeFile"))
+
+check(sharedSigningStoreFile.isFile) {
+    "Shared signing keystore missing: ${sharedSigningStoreFile.absolutePath}"
+}
+
 android {
     namespace = "com.gametime.app"
     compileSdk = flutter.compileSdkVersion
@@ -23,11 +45,18 @@ android {
         versionName = flutter.versionName
     }
 
+    signingConfigs {
+        create("sharedLocal") {
+            storeFile = sharedSigningStoreFile
+            storePassword = requiredSharedSigningProperty("storePassword")
+            keyAlias = requiredSharedSigningProperty("keyAlias")
+            keyPassword = requiredSharedSigningProperty("keyPassword")
+        }
+    }
+
     buildTypes {
         release {
-            // TODO: Add your own signing config for the release build.
-            // Signing with the debug keys for now, so `flutter run --release` works.
-            signingConfig = signingConfigs.getByName("debug")
+            signingConfig = signingConfigs.getByName("sharedLocal")
         }
     }
 }