fix(build): JellyseerStatsResponse export/import spelling + test mock type

The frontend production build (tsc -b) was failing, which blocked deployment:

- api/jellyseerr.ts exported `JellyseerrStatsResponse` (double-r) while every
  import used `JellyseerStatsResponse` (single-r) — a mismatch TS reported as
  "no exported member" (with a misleading identical-name suggestion). The
  sibling types (JellyseerStat, JellyseerRecentRequest) are single-r, so
  align the export to single-r. (tsc --noEmit missed it because the root
  tsconfig is solution-style; tsc -b builds the app project and catches it.)
- RequestsTab.test.tsx's useJellyseerrStats mock returned a partial object
  that didn't satisfy UseQueryResult's full shape; cast via a typed helper.

`npm run build` (tsc -b && vite build) now succeeds; 184/184 tests + ESLint clean.

frontend/src/api/.pi-map.index.md

@@ -2,7 +2,7 @@
 dir: frontend/src/api
 
 ## role
-Centralized API client layer providing typed functions for frontend communication with various backend services and external integrations.
+Typed API client layer that centralizes all backend communication for the frontend application across multiple service domains.
 ## parent
 index: frontend/src/.pi-map.index.md
 map: frontend/src/.pi-map.md