💰 Implement 7-day free trial for Pro subscriptions

[Melvynx]

Add a 7-day free trial period for new Pro subscribers to improve conversion rates and user experience.

Current State: Two-tier system (free/pro) with immediate payment required for Pro.

Implementation:

• Use Better Auth's built-in trial support
• Add trial fields to Subscription schema
• Update auth limits to support trial status
• Add trial UI indicators and reminders

Files to modify:

• packages/database/prisma/schema.prisma
• apps/web/src/lib/auth.ts
• apps/web/src/lib/auth-limits.ts

Priority: HIGH - Business feature for conversion improvement.