build(release): Android signing, iOS privacy manifest, store assets (Phase 7)

- Android: release keystore signing wired via gitignored key.properties (falls
  back to debug when absent). Verified: signed AAB built (signer CN=Block Seasons).
- iOS: app PrivacyInfo.xcprivacy (ATT tracking flag, device-id/usage data types,
  UserDefaults+FileTimestamp required-reason APIs) registered in the Runner target.
- Store: app-ads.txt (pub-5605900229781491), EN/KO listing copy, owner submission
  guide (privacy labels, app-ads hosting, upload/submit steps).
Secrets (keystore, key.properties) are gitignored — owner backs them up.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

android/app/build.gradle.kts

@@ -1,3 +1,6 @@
+import java.io.FileInputStream
+import java.util.Properties
+
 plugins {
     id("com.android.application")
     // START: FlutterFire Configuration
@@ -8,6 +11,15 @@ plugins {
     id("dev.flutter.flutter-gradle-plugin")
 }
 
+// Release signing is read from android/key.properties (gitignored). When that
+// file is absent (CI, a fresh clone, another machine) the release build falls
+// back to debug signing so `flutter build`/`flutter run --release` still works.
+val keystoreProperties = Properties()
+val keystorePropertiesFile = rootProject.file("key.properties")
+if (keystorePropertiesFile.exists()) {
+    keystoreProperties.load(FileInputStream(keystorePropertiesFile))
+}
+
 android {
     namespace = "com.airkjw.block_seasons"
     compileSdk = flutter.compileSdkVersion
@@ -34,11 +46,24 @@ 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")
+            signingConfig = if (keystorePropertiesFile.exists()) {
+                signingConfigs.getByName("release")
+            } else {
+                signingConfigs.getByName("debug")
+            }
         }
     }
 }