Add release-signing config plugin, README, memory of PWA parity

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

plugins/with-release-signing.js

@@ -0,0 +1,37 @@
+/* Injects a release signing config into the prebuilt android project.
+   Keystore: $HEALTH_KEYSTORE or ~/.android-keys/health-app-release.jks
+   Password: $KEYSTORE_PASSWORD or ~/.android-keys/health-app-release.password
+   Falls back to the debug keystore when neither exists. */
+const { withAppBuildGradle } = require('expo/config-plugins');
+
+const SIGNING = `        release {
+            // keystore lives outside the repo; password from env or ~/.android-keys
+            def ksPath = System.getenv("HEALTH_KEYSTORE") ?: "\${System.properties['user.home']}/.android-keys/health-app-release.jks"
+            def passFile = new File("\${System.properties['user.home']}/.android-keys/health-app-release.password")
+            def ksPass = System.getenv("KEYSTORE_PASSWORD") ?: (passFile.exists() ? passFile.text.trim() : null)
+            if (new File(ksPath).exists() && ksPass != null) {
+                storeFile file(ksPath)
+                storePassword ksPass
+                keyAlias System.getenv("KEY_ALIAS") ?: "health"
+                keyPassword ksPass
+            }
+        }
+    }`;
+
+module.exports = function withReleaseSigning(config) {
+  return withAppBuildGradle(config, (cfg) => {
+    let g = cfg.modResults.contents;
+    if (!g.includes('def ksPath')) {
+      g = g.replace(
+        /(signingConfigs \{[\s\S]*?keyPassword 'android'\n {8}\}\n)( {4}\})/,
+        `$1${SIGNING}`,
+      );
+      g = g.replace(
+        /\/\/ Caution![^\n]*\n\s*\/\/ see https:\/\/reactnative\.dev[^\n]*\n\s*signingConfig signingConfigs\.debug/,
+        'signingConfig signingConfigs.release.storeFile ? signingConfigs.release : signingConfigs.debug',
+      );
+      cfg.modResults.contents = g;
+    }
+    return cfg;
+  });
+};