scheduler: add Array Starting / Array Stopping event triggers

Two hardcoded event-triggered entries appear at the top of the scheduler
(array_started.sh / array_stopping.sh). They show an ⚡ Array Start /
⚡ Array Stop badge instead of a cron field and are enabled/disabled via
the normal toggle.

Static event scripts fire them via Unraid's event system:
- event/disks_mounted/array_start_jobs  → runs in background (non-blocking)
- event/disks_unmounting/array_stop_jobs → runs foreground (blocks until done)

vv_cron_rebuild() skips @array_* entries so they never land in the cron file.
Scripts executed on each event are managed in master.conf via
ARRAY_START_SCRIPTS and ARRAY_STOP_SCRIPTS arrays.

Plugin/usr/local/emhttp/plugins/varaverk/event/disks_unmounting/array_stop_jobs

@@ -0,0 +1,13 @@
+#!/bin/bash
+# Varaverk: run array_stopping.sh if enabled in the schedule (foreground — blocks until done).
+php -r "
+require_once '/usr/local/emhttp/plugins/varaverk/include/scheduler.php';
+\$s = vv_schedule_load();
+\$e = \$s['Orchestrators/array_stopping.sh'] ?? [];
+if (empty(\$e['enabled'])) exit(0);
+\$runner = '/usr/local/emhttp/plugins/varaverk/run_job.sh';
+\$script = SCRIPTS_DIR . '/Orchestrators/array_stopping.sh';
+if (!file_exists(\$script)) exit(0);
+\$flags = !empty(\$e['log_enabled']) ? ' --log' : '';
+passthru('bash ' . escapeshellarg(\$runner) . ' Orchestrators/array_stopping.sh ' . escapeshellarg(\$script) . \$flags);
+" 2>/dev/null