fix(admin): say what actually ages a stored account copy out

The backups page stated "Retention: 90 days", from a constant whose
comment said it matched a backup-prune job. There is no such job: nothing
deletes a stored copy by age. The weekly copy is replaced in place, one
per account; the copy taken before "Delete all data" is deleted by the
account-deletion purge when the grace window ends; an uploaded copy stays
until its account is erased.

The list now carries preWipeCopyDays (the grace window, 0 when no such
copy is taken) instead of retentionDays, and the page says exactly the
three facts above, in every language.

Also drops a re-export of the JSON import row limit nothing imports.

src/app/api/admin/backups/__tests__/route.test.ts

@@ -153,6 +153,16 @@ describe("GET /api/admin/backups — off-host freshness", () => {
     expect(byName.get("account-five")?.lastAttemptAt).toBeNull();
   });
 
+  it("states what ages a stored copy out, and invents no retention", async () => {
+    configuredMock.mockReturnValue(false);
+    findManyMock.mockResolvedValue([]);
+    vi.stubEnv("ACCOUNT_DELETION_GRACE_DAYS", "21");
+    const body = await read();
+    vi.unstubAllEnvs();
+    expect(body.preWipeCopyDays).toBe(21);
+    expect(body).not.toHaveProperty("retentionDays");
+  });
+
   it("says so when neither the environment nor the ledger knows of any upload", async () => {
     configuredMock.mockReturnValue(false);
     findManyMock.mockResolvedValue([

src/app/api/admin/backups/route.ts

@@ -38,6 +38,7 @@ import {
 import { OFFHOST_BACKUP_QUEUE } from "@/lib/jobs/offhost-backup-queue";
 import { offhostPurgeDue } from "@/lib/jobs/offhost-purge-queue";
 import { ACTIVE_ACCOUNT } from "@/lib/account-deletion/active-account";
+import { accountDeletionGraceDays } from "@/lib/account-deletion/grace";
 import {
   classifyOffhostBackup,
   OFFHOST_BACKUP_PERIOD_HOURS,
@@ -213,9 +214,11 @@ export const GET = apiHandler(async () => {
 
   const payload: BackupsList = {
     rows: list,
-    // Matches the retention window the backup-prune job enforces so the
-    // backups page states the same number the worker acts on.
-    retentionDays: 90,
+    // What ages these copies out, and nothing more: no job prunes stored
+    // copies by age. The weekly copy is replaced in place, a pre-wipe copy
+    // is deleted by the account-deletion purge when its window ends, and an
+    // uploaded copy stays until its account is erased.
+    preWipeCopyDays: accountDeletionGraceDays(),
     schedule: summariseBackupSchedule({
       scheduledCreatedAt: rows
         .filter((row) => row.type === SCHEDULED_BACKUP_TYPE)