Fix timestamps, delete requests, invoice dates and GR quantities

Apply the configured timezone to PHP and both DB connections, wrap
unwrapped ajax payloads so delete buttons reach their engines, normalise
and validate invoice due dates, reject stock quantities below the stored
4dp scale, and list stock movements across all warehouses.

app/include_header.php

@@ -18,6 +18,11 @@ if (ob_get_level() === 0) {
 ini_set('display_errors', '0');
 ini_set('log_errors', '1');
 
+// Apply the configured application timezone. Pages that only require config.php
+// (no dbconn.php) still call date() for default values such as "today", so they
+// need this too or they render a UTC date.
+require_once __DIR__ . '/assets/utils/timezone.php';
+
 // Security headers — emitted before any HTML output.
 header('X-Content-Type-Options: nosniff');
 header('X-Frame-Options: SAMEORIGIN');