Wire app-side Firebase push notifications

- Rename Android package com.example.frontend -> net.oottsecurity.app
  (namespace, applicationId, MainActivity), and enable core library
  desugaring required by flutter_local_notifications
- Configure Firebase from a committed lib/firebase_options.dart (client
  identifiers, not secrets) instead of native config files; initialize the
  push service with explicit options
- iOS: add Runner.entitlements (aps-environment) wired via CODE_SIGN_ENTITLEMENTS
  for the Runner target, and UIBackgroundModes remote-notification in Info.plist
- gitignore the unused native Firebase config files defensively

dart analyze clean; 145 frontend tests pass.

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

frontend/android/app/build.gradle.kts

@@ -6,13 +6,15 @@ plugins {
 }
 
 android {
-    namespace = "com.example.frontend"
+    namespace = "net.oottsecurity.app"
     compileSdk = flutter.compileSdkVersion
     ndkVersion = flutter.ndkVersion
 
     compileOptions {
         sourceCompatibility = JavaVersion.VERSION_17
         targetCompatibility = JavaVersion.VERSION_17
+        // flutter_local_notifications uses java.time APIs that need desugaring on older Android.
+        isCoreLibraryDesugaringEnabled = true
     }
 
     kotlinOptions {
@@ -20,8 +22,7 @@ android {
     }
 
     defaultConfig {
-        // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
-        applicationId = "com.example.frontend"
+        applicationId = "net.oottsecurity.app"
         // You can update the following values to match your application needs.
         // For more information, see: https://flutter.dev/to/review-gradle-config.
         minSdk = flutter.minSdkVersion
@@ -42,3 +43,9 @@ android {
 flutter {
     source = "../.."
 }
+
+dependencies {
+    // Backport of java.time etc. required by flutter_local_notifications (see
+    // isCoreLibraryDesugaringEnabled above).
+    coreLibraryDesugaring("com.android.tools:desugar_jdk_libs:2.1.4")
+}