Task #48: Let admins page through more than the last 100 opens

Added offset/limit pagination to the two admin app-opens drill-in
endpoints so admins can investigate spikes that span more than the
default 100 most-recent opens.

Backend (artifacts/api-server/src/routes/stats.ts):
- New parsePaging() helper validates `limit` (1..200, default 100) and
  `offset` (>=0, default 0); invalid values return 400.
- Both `/stats/admin/app-opens/by-app/:appId` and
  `/stats/admin/app-opens/by-user/:userId` accept the new params, apply
  `.limit(limit).offset(offset)`, and return `limit`, `offset`, and a
  `nextOffset` (number | null) computed from `totalCount`.
- Added a stable secondary sort (`id desc`) so paged results don't
  shuffle when timestamps tie.

Spec & client (lib/api-spec/openapi.yaml + regenerated clients):
- Added `limit`/`offset` query params and `limit`/`offset`/`nextOffset`
  response fields to AdminAppOpensByApp/AdminAppOpensByUser.
- Re-ran `pnpm --filter @workspace/api-spec run codegen`.

Frontend (artifacts/teaboy-os/src/pages/admin.tsx + locales):
- AppOpensDrillIn / UserOpensDrillIn now accumulate extra pages in
  local state and expose a "Load more" button via a shared
  LoadMoreSection footer that also shows "Showing X of Y".
- Extra pages are fetched via the generated `getAdminAppOpensByApp` /
  `getAdminAppOpensByUser` functions; accumulated state resets when
  the appId/userId or stats query params change.
- Added en/ar translations for `loadMore`, `loadMoreError`, `shownOf`.

Tests:
- New artifacts/api-server/tests/admin-app-opens-pagination.test.mjs
  covers happy-path paging for both endpoints, the default page size,
  and 400 responses for invalid limit/offset.
- All 10 api-server tests pass; full workspace typecheck passes.

lib/api-client-react/src/generated/api.schemas.ts

@@ -521,6 +521,10 @@ export interface AdminAppOpensByApp {
   rangeFrom: string;
   rangeTo: string;
   totalCount: number;
+  limit: number;
+  offset: number;
+  /** @nullable */
+  nextOffset: number | null;
   opens: AppOpenByAppEntry[];
 }
 
@@ -559,6 +563,10 @@ export interface AdminAppOpensByUser {
   rangeFrom: string;
   rangeTo: string;
   totalCount: number;
+  limit: number;
+  offset: number;
+  /** @nullable */
+  nextOffset: number | null;
   opens: AppOpenByUserEntry[];
 }
 
@@ -599,6 +607,15 @@ export type GetAdminAppOpensByAppParams = {
   range?: GetAdminAppOpensByAppRange;
   from?: string;
   to?: string;
+  /**
+   * @minimum 1
+   * @maximum 200
+   */
+  limit?: number;
+  /**
+   * @minimum 0
+   */
+  offset?: number;
 };
 
 export type GetAdminAppOpensByAppRange =
@@ -615,6 +632,15 @@ export type GetAdminAppOpensByUserParams = {
   range?: GetAdminAppOpensByUserRange;
   from?: string;
   to?: string;
+  /**
+   * @minimum 1
+   * @maximum 200
+   */
+  limit?: number;
+  /**
+   * @minimum 0
+   */
+  offset?: number;
 };
 
 export type GetAdminAppOpensByUserRange =