feat(calendar): add birthday integration from contacts service

- Add birthdaysStore to fetch and manage birthdays from contacts API
- Add BirthdayPopover component with contact details and link to contacts app
- Integrate birthdays into WeekView, MonthView, and DayView as all-day events
- Add settings for showBirthdays and showBirthdayAge toggles
- Add reactive $effect in layout to load birthdays when setting is enabled
- Add /contacts/birthdays endpoint to contacts backend
- Configure PUBLIC_CONTACTS_API_URL env variable for calendar app

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

scripts/generate-env.mjs

@@ -428,6 +428,9 @@ const APP_CONFIGS = [
 			PUBLIC_MANA_CORE_AUTH_URL: (env) => env.MANA_CORE_AUTH_URL,
 			PUBLIC_TODO_BACKEND_URL: (env) =>
 				env.TODO_BACKEND_URL || `http://localhost:${env.TODO_BACKEND_PORT || '3018'}`,
+			// Cross-app integration: Contacts service for birthdays
+			PUBLIC_CONTACTS_API_URL: (env) => `http://localhost:${env.CONTACTS_BACKEND_PORT || '3015'}`,
+			PUBLIC_CONTACTS_WEB_URL: () => 'http://localhost:5184',
 		},
 	},