feat: rebuild desktop UI to match Figma + website, hero slider improvements

- Desktop sidebar (262px, blue gradient, white pill nav), topbar (search + bell + avatar), responsive shell rewritten
- Desktop homepage: immersive hero with Ken Burns animation, pill category chips, date badge cards matching mvnew.eventifyplus.com/home
- Desktop calendar: 60/40 two-column layout with white background
- Desktop profile: full-width banner + 3-column event grids
- Desktop learn more: hero image + about/venue columns + gallery strip
- Desktop settings/contribute: polished to match design system
- Mobile hero slider: RepaintBoundary, animated dots with 44px tap targets, 5s auto-scroll, 8s post-swipe delay, shimmer loading, dynamic event type badge, human-readable dates
- Guest access: requiresAuth false on read endpoints
- Location fix: show place names instead of lat/lng coordinates
- Version 1.6.1+17

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

lib/widgets/responsive_shell.dart

@@ -0,0 +1,84 @@
+import 'package:flutter/material.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+import '../core/constants.dart';
+import 'desktop_sidebar.dart';
+import 'desktop_topbar.dart';
+
+class ResponsiveShell extends StatefulWidget {
+  final int currentIndex;
+  final ValueChanged<int> onIndexChanged;
+  final Widget child;
+  final bool showTopBar;
+
+  const ResponsiveShell({
+    Key? key,
+    required this.currentIndex,
+    required this.onIndexChanged,
+    required this.child,
+    this.showTopBar = true,
+  }) : super(key: key);
+
+  @override
+  State<ResponsiveShell> createState() => _ResponsiveShellState();
+}
+
+class _ResponsiveShellState extends State<ResponsiveShell> {
+  String _username = 'Guest';
+  String? _profileImage;
+
+  @override
+  void initState() {
+    super.initState();
+    _loadPreferences();
+  }
+
+  Future<void> _loadPreferences() async {
+    final prefs = await SharedPreferences.getInstance();
+    if (!mounted) return;
+    setState(() {
+      _username = prefs.getString('display_name') ??
+          prefs.getString('username') ??
+          'Guest';
+      _profileImage = prefs.getString('profileImage');
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return LayoutBuilder(builder: (context, constraints) {
+      final width = constraints.maxWidth;
+
+      // Mobile — no shell
+      if (width < AppConstants.desktopBreakpoint) {
+        return widget.child;
+      }
+
+      return Scaffold(
+        body: Row(
+          children: [
+            DesktopSidebar(
+              selectedIndex: widget.currentIndex,
+              onIndexChanged: widget.onIndexChanged,
+            ),
+            Expanded(
+              child: Column(
+                children: [
+                  if (widget.showTopBar)
+                    DesktopTopBar(
+                      username: _username,
+                      profileImage: _profileImage,
+                      onAvatarTap: () => widget.onIndexChanged(2),
+                    ),
+                  Expanded(
+                    child: RepaintBoundary(child: widget.child),
+                  ),
+                ],
+              ),
+            ),
+          ],
+        ),
+      );
+    });
+  }
+}