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.

lib/widgets/general/search_bar.dart

@@ -0,0 +1,185 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+
+/// 轻量级异步搜索控制器，配合 [SearchBar] 使用。
+///
+/// 替代已停维的 `flappy_search_bar` 的 `SearchBarController`。
+/// 保留泛型 `<T>` 以兼容调用方 `SearchBarController<Product>()` 写法。
+/// [replayLastSearch] 用于“加载更多 / 分页”：外部 page++ 后触发重跑上一次搜索。
+class SearchBarController<T> {
+  String lastQuery = '';
+  VoidCallback? _replay;
+
+  void _register(VoidCallback replay) {
+    _replay = replay;
+  }
+
+  /// 重新执行上一次搜索（分页加载更多时调用）。
+  void replayLastSearch() => _replay?.call();
+}
+
+/// 轻量级 Web 异步搜索栏，替代已停维的 `flappy_search_bar` 的 `SearchBar`。
+///
+/// 基本流程：输入达到 [minimumChars] 个字符后，调用 [onSearch] 取结果，
+/// 用 [onItemFound] 渲染每一条；无结果时显示 [emptyWidget]；出错显示 [onError]。
+///
+/// 注意：`searchBarController` 参数刻意使用裸类型（`SearchBarController?`），
+/// 以兼容调用方 `SearchBarController _controller = SearchBarController<Product>();`
+/// 的写法（Dart 3 sound 类型下避免泛型不变性报错）。
+class SearchBar<T> extends StatefulWidget {
+  final SearchBarController? searchBarController;
+  final int minimumChars;
+  final String? hintText;
+  final Widget? cancellationWidget;
+  final Future<List<T>> Function(String text) onSearch;
+  final Widget Function(T item, int index) onItemFound;
+  final Widget Function(dynamic error)? onError;
+  final Widget? emptyWidget;
+  final Duration debounceDuration;
+
+  const SearchBar({
+    super.key,
+    this.searchBarController,
+    this.minimumChars = 2,
+    this.hintText,
+    this.cancellationWidget,
+    required this.onSearch,
+    required this.onItemFound,
+    this.onError,
+    this.emptyWidget,
+    this.debounceDuration = const Duration(milliseconds: 350),
+  });
+
+  @override
+  State<SearchBar<T>> createState() => _SearchBarState<T>();
+}
+
+class _SearchBarState<T> extends State<SearchBar<T>> {
+  final TextEditingController _textController = TextEditingController();
+  final FocusNode _focusNode = FocusNode();
+  Timer? _debounce;
+  List<T> _results = <T>[];
+  bool _loading = false;
+  dynamic _error;
+  bool _hasSearched = false;
+
+  @override
+  void initState() {
+    super.initState();
+    widget.searchBarController?._register(_runSearch);
+    _textController.addListener(_onTextChanged);
+  }
+
+  @override
+  void dispose() {
+    _debounce?.cancel();
+    _textController.dispose();
+    _focusNode.dispose();
+    super.dispose();
+  }
+
+  void _onTextChanged() {
+    final text = _textController.text;
+    _debounce?.cancel();
+    if (text.length >= widget.minimumChars) {
+      _debounce = Timer(widget.debounceDuration, _runSearch);
+    } else if (text.isEmpty) {
+      setState(() {
+        _results = <T>[];
+        _hasSearched = false;
+        _error = null;
+      });
+    }
+  }
+
+  Future<void> _runSearch() async {
+    final query = _textController.text;
+    if (query.length < widget.minimumChars) return;
+    if (widget.searchBarController != null) {
+      widget.searchBarController!.lastQuery = query;
+    }
+    setState(() {
+      _loading = true;
+      _error = null;
+      _hasSearched = true;
+    });
+    try {
+      final results = await widget.onSearch(query);
+      if (mounted) {
+        setState(() {
+          _results = results;
+          _loading = false;
+        });
+      }
+    } catch (e) {
+      if (mounted) {
+        setState(() {
+          _error = e;
+          _loading = false;
+        });
+      }
+    }
+  }
+
+  void _cancel() {
+    _textController.clear();
+    _focusNode.unfocus();
+    setState(() {
+      _results = <T>[];
+      _hasSearched = false;
+      _error = null;
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Column(
+      children: <Widget>[
+        TextField(
+          controller: _textController,
+          focusNode: _focusNode,
+          decoration: InputDecoration(
+            hintText: widget.hintText,
+            prefixIcon: const Icon(Icons.search),
+            suffixIcon: _textController.text.isNotEmpty
+                ? GestureDetector(
+                    onTap: _cancel,
+                    child: widget.cancellationWidget ??
+                        const Icon(Icons.close, size: 20),
+                  )
+                : null,
+            border: OutlineInputBorder(
+              borderRadius: BorderRadius.circular(8),
+            ),
+            contentPadding: const EdgeInsets.symmetric(horizontal: 12),
+          ),
+        ),
+        const SizedBox(height: 8),
+        Expanded(child: _buildBody()),
+      ],
+    );
+  }
+
+  Widget _buildBody() {
+    if (_loading) {
+      return const Center(child: CircularProgressIndicator());
+    }
+    if (_error != null) {
+      return widget.onError != null
+          ? widget.onError!(_error)
+          : Center(child: Text('$_error'));
+    }
+    if (!_hasSearched) {
+      return const SizedBox.shrink();
+    }
+    if (_results.isEmpty) {
+      return widget.emptyWidget ?? const SizedBox.shrink();
+    }
+    return ListView.builder(
+      itemCount: _results.length,
+      itemBuilder: (BuildContext context, int index) =>
+          widget.onItemFound(_results[index], index),
+    );
+  }
+}