feat: Implement Stripe billing with Free and Pro subscription plans

[AlecKriebel]

Summary

• Implement complete Stripe billing system with two subscription tiers
• Free plan: 1 calendar, 1 destination, daily sync, 30-day history
• Pro plan ($8/month): Unlimited calendars, unlimited destinations, 15-minute sync, unlimited history, priority support
• Full webhook handling for subscription lifecycle events (created, updated, cancelled, payment_failed)
• Feature gating based on subscription status
• Updated billing page UI with usage stats and upgrade flow
• Updated pricing page and landing page with accurate plan information

Changes

Backend

• Updated Plan enum from FREE/PAID to FREE/PRO with comprehensive limits module (packages/shared/src/types/plan.ts)
• Added database fields for subscription tracking: stripe_subscription_id, stripe_current_period_end on orgs table
• Enhanced Stripe webhook handler to handle full subscription lifecycle:
  • customer.subscription.created - New subscription provisioning
  • customer.subscription.updated - Plan changes and renewals
  • customer.subscription.deleted - Downgrade to Free
  • invoice.payment_succeeded - Successful payment tracking
  • invoice.payment_failed - Payment failure notifications
• Created plan-gating.ts utility for feature access checks

Frontend

• Updated billing page UI (org-billing-form.tsx) to show:
  • Current plan with badge and features list
  • Usage stats with progress bars (calendars, destinations)
  • Sync frequency and priority support status
  • Upgrade CTA for Free users
• Updated pricing page with Free/Pro comparison and FAQ
• Updated landing page pricing section to reflect $8/month Pro plan

Database Migration

New migration 0002_confused_lionheart.sql adds:

• stripe_subscription_id column to orgs table
• stripe_current_period_end column to orgs table
• Unique index on stripe_subscription_id

Test plan

• Verify typecheck passes: yarn workspace web tsc --noEmit
• Apply database migration in staging
• Test Free to Pro upgrade flow via Stripe Checkout
• Test Pro subscription management via Stripe Portal
• Verify webhook events update org plan correctly
• Verify billing page displays correct usage stats
• Verify feature gating limits work as expected

Follow-ups

• Actual calendar/destination count queries will need to be implemented once those tables exist
• Email templates for upgrade/downgrade notifications may need design review

Generated with Claude Code

[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.