build: upgrade to Flutter 3.47.4 (AGP 9.1 / Gradle 9.3, iOS 15 + UIScene), refresh deps and CI

Flutter 3.24.5 -> 3.47.4 with the matching toolchain changes:

- pubspec: Dart ^3.11, Firebase core 4 / auth 6 / firestore 6 / storage 13,
  drop unused image_cropper, logging, change_app_package_name,
  pdf_widget_wrapper; pin path_provider_android <2.3 (needs NDK/CMake, not
  feasible on the ARM64 Gitea runner)
- Dart: CardTheme -> CardThemeData, replace deprecated withOpacity,
  Matrix4.scale, DropdownButtonFormField.value
- iOS: deployment target 15.0, UIScene lifecycle (AppDelegate/Info.plist),
  untrack stale Podfile.lock, add LaunchImage asset set
- Android: Gradle 9.3.1, AGP 9.1.0, Kotlin 2.4.0, google-services 4.5.0,
  layout.buildDirectory instead of removed Project.buildDir, remove manifest
  package attribute and duplicate MainActivity, kotlin.incremental=false
- CI: pin FLUTTER_VERSION in both workflows; iOS on macos-26 with SwiftPM
  disabled (CocoaPods only); Gitea job keeps cirruslabs 3.44.0 as base image
  (images discontinued) and switches the bundled Flutter SDK by git tag

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

ios/Podfile

@@ -1,4 +1,5 @@
-platform :ios, '13.0'
+# Flutter 3.47+ requires iOS 15.0 as the minimum deployment target.
+platform :ios, '15.0'
 
 # CocoaPods analytics sends network stats synchronously affecting flutter build latency.
 ENV['COCOAPODS_DISABLE_STATS'] = 'true'
@@ -37,7 +38,10 @@ post_install do |installer|
   installer.pods_project.targets.each do |target|
     flutter_additional_ios_build_settings(target)
     target.build_configurations.each do |config|
-      config.build_settings['IPHONEOS_DEPLOYMENT_TARGET'] = '13.0'
+      # Keep every pod on the same deployment target as the app so old
+      # podspecs do not drag the minimum back below what Flutter supports.
+      config.build_settings['IPHONEOS_DEPLOYMENT_TARGET'] = '15.0'
+      # Pods never need to be signed; the CI produces an unsigned IPA.
       config.build_settings['CODE_SIGNING_REQUIRED'] = 'NO'
       config.build_settings['CODE_SIGNING_ALLOWED'] = 'NO'
     end