refactor: unify error feedback system with FeedbackService and StatusBar widget

- Create FeedbackService as centralized sound/vibration dispatcher
- Create reusable StatusBar widget with StatusDotColor enum (blue/orange/green/red/yellow/amber)
- Extend SoundService with beep/error/alert sound types and loop playback
- Remove top feedback banners from both registration and boxing pages
- Route all feedback through bottom status bar per PRD requirements
- Add sound and vibration feedback to boxing module (was completely missing)
- Handle network errors with yellow status, general errors with red
- Enhance duplicate dialog with alert loop sound that stops on close
- Add beep/error/alert sound file selectors in settings page

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/widgets/status_bar.dart

@@ -0,0 +1,60 @@
+import 'package:flutter/material.dart';
+
+/// Status bar dot colors matching PRD requirements.
+enum StatusDotColor {
+  blue, // idle / waiting
+  orange, // submitting
+  green, // success
+  red, // error (invalid code / submit failure / duplicate)
+  yellow, // network error
+  amber, // warning (duplicate box number)
+}
+
+/// Reusable bottom status bar with a colored dot and text.
+class StatusBar extends StatelessWidget {
+  final StatusDotColor dotColor;
+  final String text;
+
+  const StatusBar({super.key, required this.dotColor, required this.text});
+
+  Color _resolveDotColor(BuildContext context) {
+    return switch (dotColor) {
+      StatusDotColor.blue => Colors.blue,
+      StatusDotColor.orange => Colors.orange,
+      StatusDotColor.green => Colors.green,
+      StatusDotColor.red => Colors.red,
+      StatusDotColor.yellow => Colors.yellow.shade700,
+      StatusDotColor.amber => Colors.amber,
+    };
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final colorScheme = Theme.of(context).colorScheme;
+    return Container(
+      width: double.infinity,
+      padding: const EdgeInsets.symmetric(vertical: 12, horizontal: 16),
+      color: colorScheme.surfaceContainerHighest,
+      child: Row(
+        children: [
+          Container(
+            width: 8,
+            height: 8,
+            decoration: BoxDecoration(
+              color: _resolveDotColor(context),
+              shape: BoxShape.circle,
+            ),
+          ),
+          const SizedBox(width: 8),
+          Expanded(
+            child: Text(
+              text,
+              style: const TextStyle(fontSize: 14),
+              overflow: TextOverflow.ellipsis,
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+}