style(navbar): smaller centred logo, hero clears the bar, liquid-glass backdrop

site/includes/include.php

@@ -106,5 +106,13 @@ $canonical = $GLOBALS['_canonical_override'] ?? match ($page) {
     <feBlend in="SourceGraphic" in2="grain" mode="multiply" result="mix"/>
     <feComposite in="mix" in2="SourceGraphic" operator="in"/>
   </filter>
+  <!-- Liquid glass for the navbar backdrop (style.css .header-section, Chromium):
+       soft low-frequency noise, blurred so it has no grain, drives a displacement
+       that bends the page behind the bar like uneven glass. -->
+  <filter id="nav-glass" x="0" y="0" width="100%" height="100%" color-interpolation-filters="sRGB">
+    <feTurbulence type="fractalNoise" baseFrequency=".008 .04" numOctaves="2" seed="3" result="t"/>
+    <feGaussianBlur in="t" stdDeviation="2" result="map"/>
+    <feDisplacementMap in="SourceGraphic" in2="map" scale="38" xChannelSelector="R" yChannelSelector="G"/>
+  </filter>
 </svg>
 <a href="#conteudo" class="skip-link">Saltar para o conteúdo</a>