perf: fix remaining 11 performance issues across 5 screens

Critical — Image.network → CachedNetworkImage:
- home_screen.dart: hero/carousel banner image now cached with placeholder
- profile_screen.dart: avatar and event list tile images now cached
- calendar_screen.dart: event card images now cached with placeholder

High:
- profile_screen.dart: TextEditingControllers in dialogs now properly
  disposed via .then() and after await to prevent memory leaks

Medium:
- search_screen.dart: shrinkWrap:true → ConstrainedBox(maxHeight:320) +
  ClampingScrollPhysics for smooth search result scrolling
- learn_more_screen.dart: MediaQuery.of(context) cached once per method
  instead of being called multiple times on every frame

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

lib/screens/calendar_screen.dart

@@ -1,6 +1,7 @@
 // lib/screens/calendar_screen.dart
 import 'package:flutter/material.dart';
 import 'package:intl/intl.dart';
+import 'package:cached_network_image/cached_network_image.dart';
 import '../features/events/services/events_service.dart';
 import '../features/events/models/event_models.dart';
 import 'learn_more_screen.dart';
@@ -511,7 +512,16 @@ class _CalendarScreenState extends State<CalendarScreen> {
           children: [
             ClipRRect(
               borderRadius: const BorderRadius.vertical(top: Radius.circular(14)),
-              child: imgUrl != null ? Image.network(imgUrl, height: 150, width: double.infinity, fit: BoxFit.cover, errorBuilder: (_, __, ___) => Container(height: 150, color: theme.dividerColor)) : Container(height: 150, color: theme.dividerColor, child: Icon(Icons.event, size: 44, color: theme.hintColor)),
+              child: imgUrl != null
+                  ? CachedNetworkImage(
+                      imageUrl: imgUrl,
+                      height: 150,
+                      width: double.infinity,
+                      fit: BoxFit.cover,
+                      placeholder: (_, __) => Container(height: 150, color: theme.dividerColor),
+                      errorWidget: (_, __, ___) => Container(height: 150, color: theme.dividerColor),
+                    )
+                  : Container(height: 150, color: theme.dividerColor, child: Icon(Icons.event, size: 44, color: theme.hintColor)),
             ),
             Padding(
               padding: const EdgeInsets.fromLTRB(12, 12, 12, 14),

lib/screens/home_screen.dart

@@ -1216,10 +1216,12 @@ class _HomeScreenState extends State<HomeScreen> with SingleTickerProviderStateM
                 child: SizedBox(
                   width: double.infinity,
                   child: img != null && img.isNotEmpty
-                      ? Image.network(
+                      ? CachedNetworkImage(
-                          img,
+                          imageUrl: img,
                           fit: BoxFit.cover,
-                          errorBuilder: (context, error, stackTrace) =>
+                          placeholder: (_, __) => Container(
+                              decoration: const BoxDecoration(color: Color(0xFF1A2A4A))),
+                          errorWidget: (_, __, ___) =>
                               Container(decoration: AppDecoration.blueGradientRounded(radius)),
                         )
                       : Container(

lib/screens/learn_more_screen.dart

@@ -223,9 +223,10 @@ class _LearnMoreScreenState extends State<LearnMoreScreen> {
       );
     }
 
-    final screenHeight = MediaQuery.of(context).size.height;
+    final mediaQuery = MediaQuery.of(context);
+    final screenHeight = mediaQuery.size.height;
     final imageHeight = screenHeight * 0.45;
-    final topPadding = MediaQuery.of(context).padding.top;
+    final topPadding = mediaQuery.padding.top;
 
     return Scaffold(
       backgroundColor: theme.scaffoldBackgroundColor,
@@ -355,6 +356,7 @@ class _LearnMoreScreenState extends State<LearnMoreScreen> {
   // ---------------------------------------------------------------------------
 
   Widget _buildLoadingShimmer(ThemeData theme) {
+    final shimmerHeight = MediaQuery.of(context).size.height;
     return SafeArea(
       child: Padding(
         padding: const EdgeInsets.all(20),
@@ -363,7 +365,7 @@ class _LearnMoreScreenState extends State<LearnMoreScreen> {
           children: [
             // Placeholder image
             Container(
-              height: MediaQuery.of(context).size.height * 0.42,
+              height: shimmerHeight * 0.42,
               decoration: BoxDecoration(
                 color: theme.dividerColor.withOpacity(0.3),
                 borderRadius: BorderRadius.circular(28),

lib/screens/profile_screen.dart

@@ -1,5 +1,6 @@
 import 'dart:io';
 
+import 'package:cached_network_image/cached_network_image.dart';
 import 'package:flutter/foundation.dart' show kIsWeb;
 import 'package:flutter/material.dart';
 import 'package:image_picker/image_picker.dart';
@@ -273,6 +274,7 @@ class _ProfileScreenState extends State<ProfileScreen>
     final result = await showDialog<String?>(
       context: context,
       builder: (ctx) {
+        // Note: ctl is disposed after dialog closes below
         final theme = Theme.of(ctx);
         return AlertDialog(
           title: const Text('Enter image path or URL'),
@@ -305,6 +307,7 @@ class _ProfileScreenState extends State<ProfileScreen>
       },
     );
 
+    ctl.dispose();
     if (result == null || result.isEmpty) return;
     await _saveProfile(_username, _email, result);
   }
@@ -318,6 +321,7 @@ class _ProfileScreenState extends State<ProfileScreen>
       isScrollControlled: true,
       backgroundColor: Colors.transparent,
       builder: (ctx) {
+        // nameCtl and emailCtl are disposed via .then() below
         final theme = Theme.of(ctx);
         return DraggableScrollableSheet(
           expand: false,
@@ -419,7 +423,10 @@ class _ProfileScreenState extends State<ProfileScreen>
           },
         );
       },
-    );
+    ).then((_) {
+      nameCtl.dispose();
+      emailCtl.dispose();
+    });
   }
 
   // ───────── Avatar builder (reused, with size param) ─────────
@@ -428,11 +435,14 @@ class _ProfileScreenState extends State<ProfileScreen>
     final path = _profileImage.trim();
     if (path.startsWith('http')) {
       return ClipOval(
-          child: Image.network(path,
+          child: CachedNetworkImage(
+              imageUrl: path,
               width: size,
               height: size,
               fit: BoxFit.cover,
-              errorBuilder: (_, __, ___) =>
+              placeholder: (_, __) =>
+                  Container(width: size, height: size, color: const Color(0xFFE5E7EB)),
+              errorWidget: (_, __, ___) =>
                   Icon(Icons.person, size: size / 2, color: Colors.grey)));
     }
     if (kIsWeb) {
@@ -497,11 +507,16 @@ class _ProfileScreenState extends State<ProfileScreen>
         if (imageUrl.startsWith('http')) {
           return ClipRRect(
               borderRadius: BorderRadius.circular(12),
-              child: Image.network(imageUrl,
+              child: CachedNetworkImage(
+                  imageUrl: imageUrl,
                   width: 60,
                   height: 60,
                   fit: BoxFit.cover,
-                  errorBuilder: (_, __, ___) => Container(
+                  placeholder: (_, __) => Container(
+                      width: 60,
+                      height: 60,
+                      color: const Color(0xFFE5E7EB)),
+                  errorWidget: (_, __, ___) => Container(
                       width: 60,
                       height: 60,
                       color: theme.dividerColor,

lib/screens/search_screen.dart

@@ -305,9 +305,11 @@ class _SearchScreenState extends State<SearchScreen> {
                     child: Center(child: Text('No results found', style: TextStyle(color: Colors.grey[500]))),
                   )
                 else
-                  ListView.separated(
+                  ConstrainedBox(
-                    shrinkWrap: true,
+                    constraints: const BoxConstraints(maxHeight: 320),
-                    physics: const NeverScrollableScrollPhysics(),
+                    child: ListView.separated(
+                    shrinkWrap: false,
+                    physics: const ClampingScrollPhysics(),
                     itemCount: _searchResults.length,
                     separatorBuilder: (_, __) => Divider(color: Colors.grey[200], height: 1),
                     itemBuilder: (ctx, idx) {
@@ -326,6 +328,7 @@ class _SearchScreenState extends State<SearchScreen> {
                       );
                     },
                   ),
+                  ),
               ] else ...[
                 const Text('Popular Cities', style: TextStyle(fontWeight: FontWeight.bold, fontSize: 16, color: Color(0xFF1A1A2E))),
                 const SizedBox(height: 12),