fix(api): read the error code before the status

A read-failure primitive decided from the status alone, so a 401 from a
step-up or re-proof gate would have read as an ended session and sent
the reader to sign-in. The code now decides first and the status is the
fallback for codes it does not know.

The two invitation routes answer an unknown name or e-mail with
sharing.invite.no_account. Both have a second 404 with a different next
step, and since every error now carries a code the clients match on it
instead of on the status. The status defaults move into a module the
client can import, and the contract text no longer says these arms
carry no code.

src/lib/openapi/error-codes.ts

@@ -1,4 +1,4 @@
-import { DEFAULT_ERROR_CODES } from "@/lib/api-response";
+import { DEFAULT_ERROR_CODES } from "@/lib/api/default-error-codes";
 
 /**
  * Every `meta.errorCode` the API emits, grouped by the surface that emits it.
@@ -412,6 +412,7 @@ export const ERROR_CODE_CATALOGUE: Readonly<Record<string, readonly string[]>> =
       "sharing.invite.invalid",
       "sharing.invite.invalid_scope",
       "sharing.invite.manage_browser_only",
+      "sharing.invite.no_account",
       "sharing.invite.refused",
       "sharing.invite.self",
       "sharing.not_permitted",