feat(auth): per-user UI language preference (sq default, en)

Add users.language ('sq'|'en', default 'sq'; migration 0003). Returned from
/api/auth/login and /api/auth/me (read from the DB, not the JWT — so changing it
needs no re-login). New PUT /api/auth/language for self-service. Loaded on login
and restored from any booth. Printed tickets stay Albanian (customer-facing).

packages/db/drizzle/meta/_journal.json

@@ -22,6 +22,13 @@
       "when": 1781713560438,
       "tag": "0002_panoramic_tiger_shark",
       "breakpoints": true
+    },
+    {
+      "idx": 3,
+      "version": "6",
+      "when": 1781774228086,
+      "tag": "0003_early_hawkeye",
+      "breakpoints": true
     }
   ]
 }