feat: add font size toggle functionality

- Implemented a FontSizeToggle component in HomePageClient for adjusting task font sizes in kanban views.
- Updated TaskCard to apply dynamic font size classes based on user preferences.
- Enhanced user preferences to include font size settings, defaulting to 'medium'.
- Modified TODO.md to mark the font size toggle task as complete.

services/user-preferences.ts

@@ -18,7 +18,8 @@ const DEFAULT_PREFERENCES: UserPreferences = {
     showObjectives: true,
     showFilters: true,
     objectivesCollapsed: false,
-    theme: 'dark'
+    theme: 'dark',
+    fontSize: 'medium'
   },
   columnVisibility: {
     hiddenStatuses: []