feat: implement multi-step mood logging wizard

Adds sleep/energy/positivity/self-worth tracking columns to the database
(schema v2 migration), a new 5-option StepScale widget, per-answer chips
at the top of the screen, a 2×2 activity grid chip, and a full step-by-step
wizard flow: mood → sleep (first entry today only) → energy → positivity →
self-worth → activities → review+save.

lib/shared/widgets/activity_grid.dart

@@ -9,7 +9,6 @@ class ActivityGrid extends ConsumerWidget {
   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(