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/landscape_section_header.dart

@@ -0,0 +1,58 @@
+// lib/widgets/landscape_section_header.dart
+//
+// Consistent section header for the right panel of landscape layouts.
+// Shows a title, optional subtitle, and optional trailing action widget.
+
+import 'package:flutter/material.dart';
+
+class LandscapeSectionHeader extends StatelessWidget {
+  final String title;
+  final String? subtitle;
+  final Widget? trailing;
+  final EdgeInsetsGeometry padding;
+
+  const LandscapeSectionHeader({
+    Key? key,
+    required this.title,
+    this.subtitle,
+    this.trailing,
+    this.padding = const EdgeInsets.fromLTRB(24, 24, 24, 12),
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    return Padding(
+      padding: padding,
+      child: Row(
+        crossAxisAlignment: CrossAxisAlignment.end,
+        children: [
+          Expanded(
+            child: Column(
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: [
+                Text(
+                  title,
+                  style: theme.textTheme.titleLarge?.copyWith(
+                    fontWeight: FontWeight.w700,
+                    letterSpacing: -0.3,
+                  ),
+                ),
+                if (subtitle != null) ...[
+                  const SizedBox(height: 2),
+                  Text(
+                    subtitle!,
+                    style: theme.textTheme.bodySmall?.copyWith(
+                      color: theme.textTheme.bodySmall?.color?.withOpacity(0.6),
+                    ),
+                  ),
+                ],
+              ],
+            ),
+          ),
+          if (trailing != null) trailing!,
+        ],
+      ),
+    );
+  }
+}