fix: apply same nullish detail guard to throwRawApiError (Bugbot)

The nullish detail fix from the previous commit only covered
throwApiError (SDK path). throwRawApiError (raw fetch path via
apiRequestToRegion) had the same issue: { detail: null } would
produce {"detail":null} as visible output in 403 enrichment.

Now checks typeof parsed.detail before using it, and skips the
JSON.stringify fallback for 403 errors.

Author: BYK

src/lib/api/infrastructure.ts

@@ -416,9 +416,17 @@ async function throwRawApiError(
     const text = await response.text();
     try {
       const parsed = JSON.parse(text) as { detail?: string };
-      detail = parsed.detail ?? JSON.stringify(parsed);
+      // Prefer the explicit `detail` field; fall back to the full JSON
+      // for non-403 errors (useful for debugging). For 403s, pass
+      // undefined so enrich403Detail stands alone without a noisy
+      // `{"detail":null}` prefix.
+      if (typeof parsed.detail === "string") {
+        detail = parsed.detail;
+      } else if (response.status !== 403) {
+        detail = JSON.stringify(parsed);
+      }
     } catch {
-      detail = text;
+      detail = text || undefined;
     }
   } catch {
     detail = response.statusText;