ver. 0.300: Manifest-based update system with checksum verification and file backup

Replaces the manual ZIP packaging workflow with an automated build script.
UpdateRepository now supports both manifest JSON format (new) and legacy
_sql.txt/_files.txt format (fallback), enabling a smooth transition for
existing client instances.

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

admin/templates/update/main-view.php

@@ -41,6 +41,17 @@
   </div>
 </div>
 
+<? if ( !empty( $this->log ) ): ?>
+<div class="panel">
+  <div class="panel-heading">
+    <span class="panel-title">Log ostatniej aktualizacji</span>
+  </div>
+  <div class="panel-body">
+    <pre style="max-height: 400px; overflow-y: auto; font-size: 12px;"><?= htmlspecialchars( $this->log ); ?></pre>
+  </div>
+</div>
+<? endif; ?>
+
 <div class="panel">
   <div class="panel-heading">
     <span class="panel-title">Changelog</span>