feat(varaverk): add local .plg registration; remove dev-mode cron fallback

Create varaverk.plg on flash (/boot/config/plugins/varaverk/varaverk.plg).
On boot, rebuild_cron copies it to /var/log/plugins/ so update_cron natively
picks up varaverk.cron and merges it into /etc/cron.d/root.

With the .plg in place the dev-mode direct-inject fallback in vv_cron_rebuild()
is no longer needed and has been removed.

Plugin/usr/local/emhttp/plugins/varaverk/include/scheduler.php

@@ -67,19 +67,6 @@ function vv_cron_rebuild(array $schedule): bool {
     // Write to the plugin cron file; update_cron merges all plugin *.cron files into /etc/cron.d/root.
     if (file_put_contents(CRON_FILE, implode("\n", $lines)) === false) return false;
     exec('/usr/local/sbin/update_cron');
-
-    // update_cron only picks up .plg-registered plugins. In dev (no varaverk.plg registered),
-    // inject our entries directly into the live root crontab so they take effect immediately.
-    if (!file_exists('/var/log/plugins/varaverk.plg')) {
-        $current  = shell_exec('crontab -c /etc/cron.d -l 2>/dev/null') ?: '';
-        $filtered = preg_replace('/^[^\n]*run_job\.sh[^\n]*\n?/m', '', $current);
-        $ours     = file_get_contents(CRON_FILE);
-        $combined = rtrim($filtered) . "\n\n" . $ours . "\n";
-        $tmp      = tempnam('/tmp', 'varaverk_cron_');
-        file_put_contents($tmp, $combined);
-        exec('crontab -c /etc/cron.d - < ' . escapeshellarg($tmp));
-        unlink($tmp);
-    }
     return true;
 }