Fix user detail GraphQL query

Return monthly purchase totals with the correct GraphQL scalar and align frontend queries and generated types with the upgraded schema.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

frontend/codegen.yml

@@ -9,6 +9,9 @@ generates:
             DateTime:
               input: string
               output: string
+            Decimal:
+              input: string
+              output: string
             JSONScalar:
               input: unknown
               output: "Array<{ name: string; count: number }>"
@@ -18,6 +21,9 @@ generates:
             DateTime:
               input: string
               output: string
+            Decimal:
+              input: string
+              output: string
             JSONScalar:
               input: unknown
               output: "Array<{ name: string; count: number }>"