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/smooth_star_rating.dart

@@ -0,0 +1,90 @@
+import 'package:flutter/material.dart';
+
+/// 自定义实现，替代已停维的 `smooth_star_rating` 包的 [SmoothStarRating]。
+///
+/// 保留原命名参数（`allowHalfRating`/`onRated`/`starCount`/`rating`/`size`/
+/// `filledIconData`/`color`/`borderColor`/`spacing`），调用方仅改 import 即可。
+class SmoothStarRating extends StatefulWidget {
+  final bool allowHalfRating;
+  final void Function(double)? onRated;
+  final int starCount;
+  final double rating;
+  final double size;
+  final IconData filledIconData;
+  final IconData? halfFilledIconData;
+  final IconData? defaultIconData;
+  final Color color;
+  final Color borderColor;
+  final double spacing;
+
+  const SmoothStarRating({
+    super.key,
+    this.allowHalfRating = false,
+    this.onRated,
+    this.starCount = 5,
+    this.rating = 0.0,
+    this.size = 24.0,
+    this.filledIconData = Icons.star,
+    this.halfFilledIconData,
+    this.defaultIconData,
+    this.color = Colors.orange,
+    this.borderColor = Colors.orange,
+    this.spacing = 0.0,
+  });
+
+  @override
+  State<SmoothStarRating> createState() => _SmoothStarRatingState();
+}
+
+class _SmoothStarRatingState extends State<SmoothStarRating> {
+  late double _rating;
+
+  @override
+  void initState() {
+    super.initState();
+    _rating = widget.rating;
+  }
+
+  @override
+  void didUpdateWidget(covariant SmoothStarRating oldWidget) {
+    super.didUpdateWidget(oldWidget);
+    if (oldWidget.rating != widget.rating) {
+      _rating = widget.rating;
+    }
+  }
+
+  Widget _star(int index) {
+    IconData icon;
+    Color iconColor;
+    if (index < _rating.floor()) {
+      icon = widget.filledIconData;
+      iconColor = widget.color;
+    } else if (widget.allowHalfRating &&
+        index == _rating.floor() &&
+        (_rating - index) >= 0.5) {
+      icon = widget.halfFilledIconData ?? Icons.star_half;
+      iconColor = widget.color;
+    } else {
+      icon = widget.defaultIconData ?? Icons.star_border;
+      iconColor = widget.borderColor;
+    }
+    return GestureDetector(
+      onTap: () {
+        setState(() => _rating = (index + 1).toDouble());
+        widget.onRated?.call(_rating);
+      },
+      child: Padding(
+        padding: EdgeInsets.symmetric(horizontal: widget.spacing / 2),
+        child: Icon(icon, size: widget.size, color: iconColor),
+      ),
+    );
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Row(
+      mainAxisSize: MainAxisSize.min,
+      children: List<Widget>.generate(widget.starCount, _star),
+    );
+  }
+}