audit and optimize haptic feedback across the app

Add selectionClick to settings switches, discrete slider steps, bottom
nav tabs, and expandable section headers. Fix intensity levels for cache
clear and random color (medium → light). Add lightImpact to thumbnail
long-press. Fix inconsistent search result long-press level. Replace
blanket lightImpact in updateNotification with targeted haptics at
error/warning call sites to eliminate double-firing and match severity.

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

lib/widgets/expandable_section_header.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
 import 'package:frosty/utils/context_extensions.dart';
 
 class ExpandableSectionHeader extends StatelessWidget {
@@ -24,7 +25,12 @@ class ExpandableSectionHeader extends StatelessWidget {
     final isLandscape = context.isLandscape;
 
     return InkWell(
-      onTap: onToggle,
+      onTap: onToggle != null
+          ? () {
+              HapticFeedback.selectionClick();
+              onToggle!();
+            }
+          : null,
       child: Padding(
         padding:
             padding ??