fix: remove HEAD-based site checker that caused false DOWN status

The checkAllSitesAvailability() function did HEAD requests from EasyPanel
to check sites. Many WordPress sites block HEAD or return errors, causing
all sites to show as DOWN while keeping valid response times from the
CWP collector. The CWP collector (collect-sites.sh) is the single source
of truth for site status.

Removed:
- checkSiteAvailability() and checkAllSitesAvailability() from monitoring service
- POST /api/monitor/check-sites endpoint
- api/scripts/check-sites.ts cron script

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

api/routes/monitor.ts

@@ -1,7 +1,7 @@
 /**
  * Monitor API Route
  * GET /api/monitor - Get all monitoring data
- * POST /api/monitor/check-sites - Trigger site availability check
+ * Site status comes from CWP collector (collect-sites.sh) via sync-to-db.sh
  * @author Descomplicar® | @link descomplicar.pt | @copyright 2026
  */
 import { Router } from 'express'
@@ -21,21 +21,4 @@ router.get('/', async (_req: Request, res: Response) => {
   }
 })
 
-// Trigger site availability check
-router.post('/check-sites', async (_req: Request, res: Response) => {
-  try {
-    console.log('[Monitor] Manual site check triggered')
-    const result = await monitoringService.checkAllSitesAvailability()
-    res.json({
-      success: true,
-      message: 'Site check completed',
-      ...result,
-      timestamp: new Date().toISOString()
-    })
-  } catch (error) {
-    console.error('Site check error:', error)
-    res.status(500).json({ error: 'Internal server error', message: (error as Error).message })
-  }
-})
-
 export default router