fix: serve logo locally to fix broken image on nav/footer

External URL was unreachable from tools subdomain (CSP or cross-origin block),
causing a grey placeholder rectangle. Logo now served from assets/images/ and
brightness/invert filter removed — logo is white-on-transparent, displays
correctly on dark nav and footer without filtering.

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

index.php

@@ -147,8 +147,8 @@ window.DBN_TOOLS_LANG = <?= json_encode($uiLang, JSON_UNESCAPED_UNICODE) ?>;
     <header class="lt-nav">
         <a href="https://dobetternorge.no" class="lt-nav__brand">
             <picture>
-                <source srcset="https://dobetternorge.no/assets/images/brand/logo-header.webp" type="image/webp">
-                <img class="lt-nav__logo" src="https://dobetternorge.no/assets/images/brand/logo-header.png" alt="Do Better Norge" width="140" height="36" loading="eager">
+                <source srcset="assets/images/logo-header.webp" type="image/webp">
+                <img class="lt-nav__logo" src="assets/images/logo-header.png" alt="Do Better Norge" width="140" height="36" loading="eager">
             </picture>
             <span class="lt-nav__badge">Legal Tools</span>
         </a>