feat: add DI support and tests for remaining billing functions

Auto-topup functions:
- validateAutoTopupStatus: DI for db and stripeServer
- checkAndTriggerAutoTopup: DI for db, stripe, calculateUsageAndBalance, etc.
- checkAndTriggerOrgAutoTopup: DI for db, stripe, org billing functions

Stripe metering:
- reportPurchasedCreditsToStripe: DI for db, stripe, shouldAttemptStripeMetering

Grant credits helpers:
- getPreviousFreeGrantAmount: DI for db
- calculateTotalReferralBonus: DI for db
- processAndGrantCredit: DI for grantCreditFn and logSyncFailure

New test files:
- auto-topup.test.ts: 19 tests for auto-topup DI
- stripe-metering.test.ts: 12 tests for stripe metering DI
- Updated grant-credits.test.ts with helper function tests

Type improvements:
- Added BillingOrganization type to contracts/billing.ts
- Added org query to BillingDbConnection interface
- Added org support to mock-db.ts

Author: brandonkachen

common/src/testing/mock-db.ts

@@ -21,6 +21,7 @@
 import type { GrantType } from '../types/grant'
 import type {
   BillingDbConnection,
+  BillingOrganization,
   BillingUser,
   CreditGrant,
   FindFirstParams,
@@ -425,6 +426,7 @@ export function createMockDb(config: MockDbConfig = {}): BillingDbConnection {
     query: {
       user: createTableQuery<BillingUser>(users as BillingUser[]),
       creditLedger: createTableQuery<CreditGrant>(creditGrants as CreditGrant[]),
+      org: createTableQuery<BillingOrganization>(organizations as BillingOrganization[]),
     },
   }
 }

common/src/types/contracts/billing.ts

@@ -43,6 +43,19 @@ export type Referral = {
   credits: number
 }
 
+/**
+ * Organization record fields relevant to billing
+ */
+export type BillingOrganization = {
+  id: string
+  auto_topup_enabled: boolean | null
+  auto_topup_threshold: number | null
+  auto_topup_amount: number | null
+  stripe_customer_id: string | null
+  current_period_start: Date | null
+  current_period_end: Date | null
+}
+
 // ============================================================================
 // Query Builder Types for Type-Safe Database Operations
 // ============================================================================
@@ -208,6 +221,8 @@ export type BillingDbConnection = {
     user: TableQuery<BillingUser>
     /** Query the creditLedger table */
     creditLedger: TableQuery<CreditGrant>
+    /** Query the org table (for organization billing) */
+    org: TableQuery<BillingOrganization>
   }
 }