feat(referral): integrate referral system frontend

- Add referral code input to RegisterPage with live validation
- Create ReferralWidget for dashboard with stats, code sharing, and tier display
- Extend authService.signUp to accept optional referralCode parameter
- Add validateReferralCode function to authStore
- Create referrals.ts API service for frontend
- Add 'referral' widget type to dashboard configuration
- Fix drizzle.config.ts to include 'referrals' schema filter

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

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

services/mana-core-auth/drizzle.config.ts

@@ -7,7 +7,7 @@ export default defineConfig({
 	dbCredentials: {
 		url: process.env.DATABASE_URL || 'postgresql://manacore:devpassword@localhost:5432/manacore',
 	},
-	schemaFilter: ['auth', 'credits', 'public'],
+	schemaFilter: ['auth', 'credits', 'referrals', 'public'],
 	verbose: true,
 	strict: true,
 });