feat(backup): admin UI with admin-chosen target directory

The backup destination is now chosen by the on-site admin in the UI (Setup ->
Backup), not a server env var. An env-pinned target defeats the purpose: the admin
can't point backups at a freshly-plugged USB or a NAS mount without editing .env
and restarting. The encryption key stays a server secret.

Target storage:
- New site_config.backup_target_dir (migration 0016, nullable; null = not
  configured). BackupService reads it fresh each run, so a UI change takes effect
  with no restart. Only BACKUP_KEY stays env -- a key must never live in the DB it
  backs up.

Routes:
- PUT /api/backup/config  -- set/clear the target (backup:update; upserts id=1).
- POST /api/backup/test   -- probe a candidate path server-side (exists / is a
  directory / writable) so the admin gets feedback before relying on it.
- status() now exposes targetDir + keyPresent, so the UI distinguishes
  'no target set' from 'BACKUP_KEY missing'.

UI (apps/web/src/BackupSettings.tsx):
- A Setup -> Backup tab (gated backup:read): an editable target-path field with a
  Test-target probe (localized ok/missing/not-a-dir/not-writable), Save, the status
  panel (config state, last-run size/pruned/error, a distinct amber missing-key
  warning), a Back up now button, and the restore-is-out-of-band note. Full i18n
  (sq + en); nav.backup.
- API client: fetchBackupStatus / setBackupTarget / testBackupTarget / runBackup.

Also includes a small in-progress copy trim to the setup-intro i18n strings.

Verified live with Playwright: typed a path -> Test reported writable -> Save
persisted it -> status reflected it and showed the key-missing warning. Whole
monorepo build/lint/test green. Wiki backup-recovery + open-question #5 updated.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

apps/web/src/router.tsx

@@ -42,6 +42,7 @@ import { UsersManager } from "./UsersManager.js";
 import { RolesManager } from "./RolesManager.js";
 import { ShiftsHistory } from "./ShiftsHistory.js";
 import { LogsViewer } from "./LogsViewer.js";
+import { BackupSettings } from "./BackupSettings.js";
 import { RecycleBin } from "./RecycleBin.js";
 import { Profile } from "./Profile.js";
 // Reports pulls in Recharts (~heavy) — lazy-loaded so it stays OUT of the booth's
@@ -106,6 +107,7 @@ function SetupLayout() {
         {show("role:read") && <SetupTab to="/setup/roles" label={t("nav.roles")} />}
         {show("recyclebin:read") && <SetupTab to="/setup/recycle-bin" label={t("nav.recycleBin")} />}
         {show("log:read") && <SetupTab to="/setup/logs" label={t("nav.logs")} />}
+        {show("backup:read") && <SetupTab to="/setup/backup" label={t("nav.backup")} />}
       </nav>
       <Outlet />
     </div>
@@ -444,6 +446,7 @@ function RootLayout() {
             show("user:read") ||
             show("role:read") ||
             show("recyclebin:read") ||
+            show("backup:read") ||
             show("shift:read")) && <NavLink to="/setup" label={t("nav.setup")} />}
         </nav>
         <div className="ml-auto flex items-center gap-3">
@@ -694,6 +697,14 @@ const logsRoute = createRoute({
   component: LogsViewer,
 });
 
+// Encrypted DB backup — status + manual run. Gated by backup:read (run by backup:create).
+const backupRoute = createRoute({
+  getParentRoute: () => setupRoute,
+  path: "backup",
+  beforeLoad: ({ context }) => requirePerm("backup:read")(context),
+  component: BackupSettings,
+});
+
 // My profile — self-service for ANY signed-in user (no permission gate). Edits only
 // the caller's own name/email/password. See Profile.tsx and routes/auth.ts.
 const profileRoute = createRoute({
@@ -726,6 +737,7 @@ const routeTree = rootRoute.addChildren([
     rolesRoute,
     recycleBinRoute,
     logsRoute,
+    backupRoute,
   ]),
 ]);