feat: wire up app shell, log mood screen, and fix Android build

- Bootstrap ProviderScope in main.dart and move App to app.dart with light/dark theming
- Add initial LogMoodScreen with mood entry flow and shared activity/mood widgets
- Add kIsWeb guard in app_database.dart for drift web support
- Enable Android core library desugaring required by flutter_local_notifications 21.x
- Guard all async notifier state assignments with ref.mounted checks to prevent
  use-after-dispose errors when providers are auto-disposed mid-operation

lib/shared/widgets/activity_grid.dart

@@ -0,0 +1,42 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import '../../core/providers/activity_provider.dart';
+
+class ActivityGrid extends ConsumerWidget {
+  const ActivityGrid({super.key});
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final activitiesAsync = ref.watch(activitiesProvider);
+    final selected = ref.watch(selectedActivitiesProvider);
+    final theme = Theme.of(context);
+
+    return activitiesAsync.when(
+      data: (activities) => Wrap(
+        spacing: 8,
+        runSpacing: 8,
+        children: activities.map((a) {
+          final isSelected = selected.contains(a.id);
+          return FilterChip(
+            avatar: Text(
+              String.fromCharCode(a.iconCodepoint),
+              style: const TextStyle(fontFamily: 'MaterialIcons'),
+            ),
+            label: Text(a.name),
+            selected: isSelected,
+            onSelected: (_) =>
+                ref.read(selectedActivitiesProvider.notifier).toggle(a.id),
+            selectedColor: Color(
+              int.parse(a.colourHex.replaceFirst('#', '0xFF')),
+            ).withOpacity(0.2),
+            checkmarkColor: Color(
+              int.parse(a.colourHex.replaceFirst('#', '0xFF')),
+            ),
+          );
+        }).toList(),
+      ),
+      loading: () => const Center(child: CircularProgressIndicator()),
+      error: (e, _) => Text('Error loading activities: $e'),
+    );
+  }
+}

lib/shared/widgets/mood_selector.dart

@@ -0,0 +1,53 @@
+import 'package:flutter/material.dart';
+
+class MoodSelector extends StatelessWidget {
+  final int selected;
+  final List<String> emojis;
+  final List<String> labels;
+  final List<Color> colors;
+  final ValueChanged<int> onChanged;
+
+  const MoodSelector({
+    super.key,
+    required this.selected,
+    required this.emojis,
+    required this.labels,
+    required this.colors,
+    required this.onChanged,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return Row(
+      mainAxisAlignment: MainAxisAlignment.spaceEvenly,
+      children: List.generate(5, (i) {
+        final level = i + 1;
+        final isSelected = selected == level;
+        return GestureDetector(
+          onTap: () => onChanged(level),
+          child: AnimatedContainer(
+            duration: const Duration(milliseconds: 200),
+            curve: Curves.easeOut,
+            width: isSelected ? 64 : 52,
+            height: isSelected ? 64 : 52,
+            decoration: BoxDecoration(
+              color:
+                  isSelected ? colors[i].withOpacity(0.15) : Colors.transparent,
+              shape: BoxShape.circle,
+              border: Border.all(
+                color: isSelected ? colors[i] : Colors.transparent,
+                width: 2,
+              ),
+            ),
+            child: Center(
+              child: Text(
+                emojis[i],
+                style: TextStyle(fontSize: isSelected ? 36 : 28),
+              ),
+            ),
+          ),
+        );
+      }),
+    );
+  }
+}