feat: Phase 2 — upgrade deps to null-safe, replace deprecated packages

- pubspec: bump all maintained deps to null-safe latest; flutter pub get resolves
- Remove 12 packages (0-ref or no null-safe): splashscreen, flappy_search_bar,
  searchable_dropdown, share, platform_detect, flutter_inappwebview, countdown,
  gender_selection, flutter_dash, smooth_star_rating, hovering, ffi
- Add flutter_rating_bar
- Keep discontinued-but-null-safe for now (Phase 5): pull_to_refresh, hive, catcher
- New null-safe custom components (API-compatible, callers change only imports):
  utils/countdown.dart, widgets/general/{hover_widget,gender_selection,
  smooth_star_rating,search_bar}.dart
- main.dart: drop dead SplashScreen _buildBody + _to field
- 23 consuming files: swap deprecated imports to local components

Null-safety migration + upgraded-API adaptation = Phase 3.

windows/flutter/generated_plugin_registrant.cc

@@ -7,11 +7,17 @@
 #include "generated_plugin_registrant.h"
 
 #include <catcher/catcher_plugin.h>
-#include <url_launcher_windows/url_launcher_plugin.h>
+#include <file_selector_windows/file_selector_windows.h>
+#include <geolocator_windows/geolocator_windows.h>
+#include <url_launcher_windows/url_launcher_windows.h>
 
 void RegisterPlugins(flutter::PluginRegistry* registry) {
   CatcherPluginRegisterWithRegistrar(
       registry->GetRegistrarForPlugin("CatcherPlugin"));
-  UrlLauncherPluginRegisterWithRegistrar(
-      registry->GetRegistrarForPlugin("UrlLauncherPlugin"));
+  FileSelectorWindowsRegisterWithRegistrar(
+      registry->GetRegistrarForPlugin("FileSelectorWindows"));
+  GeolocatorWindowsRegisterWithRegistrar(
+      registry->GetRegistrarForPlugin("GeolocatorWindows"));
+  UrlLauncherWindowsRegisterWithRegistrar(
+      registry->GetRegistrarForPlugin("UrlLauncherWindows"));
 }