nextcloud: make the mesh's own account match its secret when Nextcloud refuses it, and back off a refusal that stays (issue 1253)

The image creates NEXTCLOUD_ADMIN_USER only on a fresh install. novox's
instance was installed before the mesh adopted it, so mesh-admin was never
created there, and the shares poll asked Nextcloud every minute with a login
that cannot pass: 401, then Nextcloud's brute-force throttle (429), which
also held the backup before a delivery.

On a refused login the client now adds the account through occ (admin
group), or sets its password to the module's own secret, passing it by
OC_PASS so it is on no argv, and asks once more. A refusal that stays is
said once and the poll backs off from 5 minutes to an hour instead of nine
lines of XML every minute. An empty setting no longer becomes an empty name.

modules/nextcloud/index.ts

@@ -9,7 +9,7 @@
 // existing user and share as freshly created.
 
 import { emit } from "@novox/mesh-sdk/events";
-import { NextcloudClient } from "./client.js";
+import { Backoff, NextcloudClient, pollSharesGuarded } from "./client.js";
 
 // Constructed lazily so an unconfigured node (no admin password) loads this entrypoint without
 // crashing the events host — it simply watches nothing.
@@ -69,7 +69,11 @@ if (nextcloud) {
     run();
   };
   tick(pollUsers);
-  tick(pollShares);
+  // A refused login is said once and the shares are left alone for 5 minutes, doubling to an hour,
+  // instead of a refusal every minute that Nextcloud's brute-force protection then throttles
+  // (novox/hq issue 1253).
+  const sharesBackoff = new Backoff(5 * 60_000, 60 * 60_000);
+  tick((c) => pollSharesGuarded(c, sharesBackoff, pollShares));
   tick(applyOnlyOffice);
   console.log("[nextcloud] watching users, shares and onlyoffice settings");
 }