chore(release): beta packaging — signing, changelog, store metadata, scale test

- Android release signing reads a gitignored key.properties, falling back
  to debug keys so contributors can still build --release.
- CHANGELOG.md (human, newest-first) + Fastlane/F-Droid metadata (en/es)
  with descriptions derived from docs/intro.md.
- docs/release.md: the by-hand build + manual smoke checklist (no CI yet).
- inventory_scale_test guards the list query against N+1 at 3000 varieties.

apps/app_seeds/android/app/build.gradle.kts

@@ -1,3 +1,6 @@
+import java.util.Properties
+import java.io.FileInputStream
+
 plugins {
     id("com.android.application")
     id("kotlin-android")
@@ -5,6 +8,17 @@ plugins {
     id("dev.flutter.flutter-gradle-plugin")
 }
 
+// Release signing is opt-in: drop a `key.properties` (gitignored) next to this
+// module's android/ dir to sign release builds with your own keystore. Without
+// it, release builds fall back to debug keys so contributors can still run
+// `flutter run --release`. See docs/release.md.
+val keystoreProperties = Properties()
+val keystorePropertiesFile = rootProject.file("key.properties")
+val hasReleaseKeystore = keystorePropertiesFile.exists()
+if (hasReleaseKeystore) {
+    keystoreProperties.load(FileInputStream(keystorePropertiesFile))
+}
+
 android {
     namespace = "org.comunes.tane"
     compileSdk = flutter.compileSdkVersion
@@ -20,7 +34,6 @@ android {
     }
 
     defaultConfig {
-        // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
         applicationId = "org.comunes.tane"
         // You can update the following values to match your application needs.
         // For more information, see: https://flutter.dev/to/review-gradle-config.
@@ -30,11 +43,27 @@ android {
         versionName = flutter.versionName
     }
 
+    signingConfigs {
+        if (hasReleaseKeystore) {
+            create("release") {
+                keyAlias = keystoreProperties["keyAlias"] as String
+                keyPassword = keystoreProperties["keyPassword"] as String
+                storeFile = keystoreProperties["storeFile"]?.let { file(it) }
+                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")
+            // Sign with the real release keystore when key.properties is present,
+            // otherwise fall back to debug keys so `flutter run --release` works
+            // for contributors without the signing material.
+            signingConfig = if (hasReleaseKeystore) {
+                signingConfigs.getByName("release")
+            } else {
+                signingConfigs.getByName("debug")
+            }
         }
     }
 }