Add accounts, members, and processor-agnostic payment linking

- account table (billing entity, soft-delete, company-scoped)
- member table (people on an account, is_minor from DOB)
- account_processor_link table (maps accounts to any payment
  processor — stripe, global_payments — instead of stripe_customer_id
  directly on account)
- Full CRUD routes + search (name, email, phone, account_number)
- Member routes nested under accounts with isMinor auto-calculation
- Zod validation schemas in @forte/shared
- 19 tests passing

packages/shared/src/schemas/index.ts

@@ -1,2 +1,17 @@
 export { UserRole, RegisterSchema, LoginSchema } from './auth.schema.js'
 export type { RegisterInput, LoginInput } from './auth.schema.js'
+
+export {
+  BillingMode,
+  AccountCreateSchema,
+  AccountUpdateSchema,
+  MemberCreateSchema,
+  MemberUpdateSchema,
+  AccountSearchSchema,
+} from './account.schema.js'
+export type {
+  AccountCreateInput,
+  AccountUpdateInput,
+  MemberCreateInput,
+  MemberUpdateInput,
+} from './account.schema.js'