docs(api): set problem documentation namespace

docs/API-SPEC.md

@@ -170,7 +170,7 @@ Every non-SSE error response uses RFC 9457 `application/problem+json` with:
 
 ```json
 {
-  "type": "https://api.zarinpal.example/problems/validation-error",
+  "type": "https://zarinpal.amiirkhl.ir/docs/errors/validation-error",
   "title": "Request validation failed",
   "status": 422,
   "detail": "One or more request values are invalid.",
@@ -277,11 +277,11 @@ Correlate `requestId`, authenticated user/merchant internal ids, run id, section
 - CSV uses UTF-8 with a BOM, Persian column names separated by normal spaces, and Persian status labels. Numeric cells remain plain calculation-safe numbers and timestamps remain UTC ISO values.
 - Analytics-access and CSV-export audit records are retained for 90 days and are accessible only to explicitly authorized backend operators; the MVP exposes no merchant audit-history surface.
 - Detail responses and CSV exports show the existing opaque source terminal reference as `شناسه پایانه`; it is tenant-scoped trace data and never an authorization input.
+- RFC 9457 problem `type` URIs use `https://zarinpal.amiirkhl.ir/docs/errors/{error-slug}` and resolve to human-readable error documentation.
 
 ## Remaining product questions
 
-1. Choose the production base URI used for dereferenceable Problem Details `type` documentation; `https://api.zarinpal.example/problems/...` is a non-production placeholder in the draft contract.
-2. Approve or revise the proposed public-edge request limits: 16 KiB for JSON bodies and 8 KiB for the request target/query string.
+1. Approve or revise the proposed public-edge request limits: 16 KiB for JSON bodies and 8 KiB for the request target/query string.
 
 ## Standards references