feat(common): add referral_legacy grant type and update priorities

- Add referral_legacy to GrantType union and GrantTypeValues array
- Update GRANT_PRIORITIES: referral_legacy=30 (consumed first, renews monthly), referral=50 (one-time, preserved longer)
- Add consumption order comment for clarity

Author: brandonkachen

common/src/constants/grant-priorities.ts

@@ -1,9 +1,11 @@
 import type { GrantType } from '@codebuff/common/types/grant'
 
+// Lower = consumed first
 export const GRANT_PRIORITIES: Record<GrantType, number> = {
   free: 20,
-  referral: 30,
+  referral_legacy: 30, // Legacy recurring referrals (renews monthly, consumed first)
   ad: 40,
+  referral: 50, // One-time referrals (never expires, preserved longer)
   admin: 60,
   organization: 70,
   purchase: 80,

common/src/types/grant.ts

@@ -1,6 +1,7 @@
 export type GrantType =
   | 'free'
   | 'referral'
+  | 'referral_legacy'
   | 'purchase'
   | 'admin'
   | 'organization'
@@ -9,6 +10,7 @@ export type GrantType =
 export const GrantTypeValues = [
   'free',
   'referral',
+  'referral_legacy',
   'purchase',
   'admin',
   'organization',