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>

android/build.gradle

@@ -1,4 +1,3 @@
-
 allprojects {
     repositories {
         google()
@@ -6,28 +5,18 @@ allprojects {
     }
 }
 
-rootProject.buildDir = '../build'
+// Keep all Gradle outputs under <repo>/build so the Flutter CLI finds the APKs.
+// (Project.buildDir was removed in Gradle 9 -> use layout.buildDirectory.)
+def newBuildDir = rootProject.layout.buildDirectory.dir("../../build").get()
+rootProject.layout.buildDirectory.value(newBuildDir)
+
 subprojects {
-    project.buildDir = "${rootProject.buildDir}/${project.name}"
-}
-subprojects {
-    
-    // Inject namespace into plugins that don't have it (required for AGP 8+)
-    afterEvaluate { project ->
-        if (project.hasProperty('android')) {
-            project.android {
-                if (namespace == null) {
-                    namespace project.group
-                }
-            }
-        }
-    }
+    project.layout.buildDirectory.value(newBuildDir.dir(project.name))
 }
 subprojects {
     project.evaluationDependsOn(':app')
 }
 
 tasks.register("clean", Delete) {
-    delete rootProject.buildDir
+    delete rootProject.layout.buildDirectory
 }
-