ci: implement Android build and test stage

- Add .gitea/workflows/ci.yml: lint -> test -> build-android -> build-ios pipeline
  - Flutter 3.41.x aligned with devcontainer (was 3.27.x)
  - Java 17 (temurin) with Gradle build cache
  - flutter precache --android + SDK license acceptance (CI crash fixes)
  - Conditional release signing via ANDROID_KEYSTORE_* secrets
  - Pre-build gates (analyze + test) skip expensive build on failure
  - Conditional whitelabel build script (only when theme.json exists)
  - APK + AAB artifact upload (90-day retention)
- Add .gitea/workflows/release.yml: tag-triggered release pipeline
  - Lint -> test -> build-android -> build-ios -> publish-release
  - Gitea Release creation with APK attachment
  - Fixed Gitea API auth (was leaking placeholder '***' token)
  - Apple signing support via APPLE_CERTIFICATE_* secrets
- Update android/app/build.gradle.kts: conditional release signing
  - signingConfigs.release block loads from key.properties when present
  - Falls back to debug signing when key.properties absent
  - Backward compatible with local dev (no secrets required)

android/app/build.gradle.kts

@@ -12,6 +12,13 @@ dependencies {
     implementation("androidx.media:media:1.7.0")
 }
 
+// Load release signing properties if key.properties exists (set by CI pipeline)
+val keystorePropertiesFile = rootProject.file("key.properties")
+val keystoreProperties = java.util.Properties()
+if (keystorePropertiesFile.exists()) {
+    keystoreProperties.load(java.io.FileInputStream(keystorePropertiesFile))
+}
+
 android {
     namespace = "com.example.kryz_go_flutter"
     compileSdk = flutter.compileSdkVersion
@@ -37,11 +44,25 @@ android {
         versionName = flutter.versionName
     }
 
+    signingConfigs {
+        create("release") {
+            if (keystorePropertiesFile.exists()) {
+                keyAlias = keystoreProperties["keyAlias"] as String
+                keyPassword = keystoreProperties["keyPassword"] as String
+                storeFile = file(keystoreProperties["storeFile"] as String)
+                storePassword = keystoreProperties["storePassword"] as String
+            }
+        }
+    }
+
     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")
+            // Use release signing if key.properties exists, otherwise fall back to debug.
+            if (keystorePropertiesFile.exists()) {
+                signingConfig = signingConfigs.getByName("release")
+            } else {
+                signingConfig = signingConfigs.getByName("debug")
+            }
         }
     }
 }