refactor: Replace interface{} with any alias and optimize string formatting with fmt.Appendf

- Replace map[string]interface{} with map[string]any in GraphQL, metrics, payment gateway, and webhook handlers
- Replace []byte(fmt.Sprintf()) with fmt.Appendf(nil, ...) for cursor encoding in GraphQL resolvers and tests
- Replace strings.HasPrefix/TrimPrefix with strings.CutPrefix for webhook signature parsing
- Replace stripe.Int64/Bool with new() constructor for Stripe payment parameters
- Rename Error

apps/api-server/internal/graphql/generated.go

@@ -370,6 +370,6 @@ func (e *executableSchema) Exec(ctx context.Context) graphql.ResponseHandler {
 	return nil
 }
 
-func (e *executableSchema) Extensions() map[string]interface{} {
-	return map[string]interface{}{}
+func (e *executableSchema) Extensions() map[string]any {
+	return map[string]any{}
 }