feat(backup): admin-tunable retention + BACKUP_KEY as a Komodo secret

Retention (keep-last / keep-daily-days) is operational policy the on-site admin
should tune, not a server env var requiring a redeploy -- same reasoning that moved
the target directory to the UI.

- Migration 0017: site_config.backup_keep_last + backup_keep_daily_days (nullable;
  null = code default 7 / 30 per field).
- BackupService reads retention fresh each run; status() exposes keepLast +
  keepDailyDays. DEFAULT_BACKUP_RETENTION is now a pure code default (env reads gone).
- PUT /api/backup/config accepts keepLast / keepDailyDays (non-negative int, or null
  to reset to default; 400 on negative).
- UI: two retention fields on the Backup config card; one Save covers target +
  retention. i18n sq + en.

BACKUP_KEY wired into Komodo:
- komodo/resources.toml: BACKUP_KEY=[[park_buzi_backup_key]] (per-booth secret,
  alongside JWT / signing keys).
- komodo/.env.komodo.example: documents it as the ONLY backup env var -- escrow it
  offsite alongside EVENT_SIGNING_KEY (recovery needs both); target + retention are
  admin-chosen in the UI / DB, not env. Server .env.example trimmed to just BACKUP_KEY.

Also carries the small in-progress setup-intro i18n copy trim.

Tests: 218 server tests green, incl. retention persist / reset-to-default / reject-
negative and the updated status shape. Migration applies cleanly (needed a
statement-breakpoint between the two ALTERs). Wiki backup-recovery updated.

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

apps/web/src/BackupSettings.tsx

@@ -5,7 +5,7 @@ import {
   ApiError,
   fetchBackupStatus,
   runBackup,
-  setBackupTarget,
+  setBackupConfig,
   testBackupTarget,
   type BackupStatus,
   type TargetCheck,
@@ -56,6 +56,8 @@ export function BackupSettings() {
   const qc = useQueryClient();
   const [toast, setToast] = useState<{ kind: "ok" | "err"; msg: string } | null>(null);
   const [target, setTarget] = useState("");
+  const [keepLast, setKeepLast] = useState("");
+  const [keepDaily, setKeepDaily] = useState("");
   const [check, setCheck] = useState<{ kind: "ok" | "err"; msg: string } | null>(null);
 
   const q = useQuery({
@@ -65,13 +67,22 @@ export function BackupSettings() {
   });
   const status = q.data;
 
-  // Seed the editable field from the saved value once it loads (and when it changes server-side).
+  // Seed the editable fields from the saved values once they load (and on server-side change).
   useEffect(() => {
-    if (status) setTarget(status.targetDir ?? "");
-  }, [status?.targetDir]);
+    if (status) {
+      setTarget(status.targetDir ?? "");
+      setKeepLast(String(status.keepLast));
+      setKeepDaily(String(status.keepDailyDays));
+    }
+  }, [status?.targetDir, status?.keepLast, status?.keepDailyDays]);
 
   const save = useMutation({
-    mutationFn: () => setBackupTarget(target.trim() || null),
+    mutationFn: () =>
+      setBackupConfig({
+        targetDir: target.trim() || null,
+        keepLast: keepLast.trim() === "" ? null : Number(keepLast),
+        keepDailyDays: keepDaily.trim() === "" ? null : Number(keepDaily),
+      }),
     onSuccess: (next) => {
       setToast({ kind: "ok", msg: t("backup.saved") });
       setCheck(null);
@@ -101,7 +112,10 @@ export function BackupSettings() {
     },
   });
 
-  const dirty = (status?.targetDir ?? "") !== target.trim();
+  const dirty =
+    (status?.targetDir ?? "") !== target.trim() ||
+    String(status?.keepLast ?? "") !== keepLast.trim() ||
+    String(status?.keepDailyDays ?? "") !== keepDaily.trim();
 
   return (
     <div className="">
@@ -134,8 +148,9 @@ export function BackupSettings() {
         </div>
       )}
 
-      {/* Target directory — the admin-chosen destination. */}
+      {/* Config — admin-chosen destination + retention policy. */}
       <div className="card mb-3 p-4">
+        {/* Target directory + its Test probe. */}
         <div className="field">
           <span className="label">{t("backup.targetLabel")}</span>
           <div className="flex flex-wrap items-center gap-2">
@@ -156,17 +171,6 @@ export function BackupSettings() {
             >
               {t("backup.test")}
             </button>
-            <button
-              type="button"
-              className="btn btn-primary btn-sm"
-              disabled={save.isPending || !dirty}
-              onClick={() => {
-                setToast(null);
-                save.mutate();
-              }}
-            >
-              {t("backup.save")}
-            </button>
           </div>
           <span className="mt-1 text-[0.6875rem] text-term-muted">{t("backup.targetHint")}</span>
           {check && (
@@ -175,6 +179,46 @@ export function BackupSettings() {
             </span>
           )}
         </div>
+
+        {/* Retention — admin-tuned policy (how many backups to keep at the target). */}
+        <div className="mt-4 flex flex-wrap items-start gap-6">
+          <div className="field">
+            <span className="label">{t("backup.keepLastLabel")}</span>
+            <input
+              type="number"
+              min={0}
+              className="input w-28"
+              value={keepLast}
+              onChange={(e) => setKeepLast(e.target.value)}
+            />
+            <span className="mt-1 text-[0.6875rem] text-term-muted">{t("backup.keepLastHint")}</span>
+          </div>
+          <div className="field">
+            <span className="label">{t("backup.keepDailyLabel")}</span>
+            <input
+              type="number"
+              min={0}
+              className="input w-28"
+              value={keepDaily}
+              onChange={(e) => setKeepDaily(e.target.value)}
+            />
+            <span className="mt-1 text-[0.6875rem] text-term-muted">{t("backup.keepDailyHint")}</span>
+          </div>
+        </div>
+
+        <div className="mt-4 flex items-center gap-3">
+          <button
+            type="button"
+            className="btn btn-primary btn-sm"
+            disabled={save.isPending || !dirty}
+            onClick={() => {
+              setToast(null);
+              save.mutate();
+            }}
+          >
+            {t("backup.save")}
+          </button>
+        </div>
       </div>
 
       <div className="card p-4">