feat: replace static logo with dynamic header text block in app layout

- Split header padding into individual properties (top, left, right) in base.css
- Reduce logo font size from 1.5em to 1.2em in base.css
- Hide static "Snek" logo div with inline display:none in app.html
- Add new logo div with block header_text template block in app.html
- Move chat header h2 from web.html into the new header_text block in app.html

src/snek/templates/app.html

@@ -21,7 +21,9 @@
 </head>
 <body>
   <header>
-    <div class="no-select logo">Snek</div>
+    <div class="no-select logo" style="display:none">Snek</div>
+    
+    <div class="logo">{% block header_text %}{% endblock %}</div>
     <nav class="no-select">
       <a class="no-select" href="/web.html">🏠</a>
       <a class="no-select" href="/search-user.html">🔍</a>
@@ -30,6 +32,7 @@
       <a class="no-select" href="#">⚙️</a>
       <a class="no-select" href="/logout.html">🔒</a>
     </nav>
+
   </header>
   <main>
     {% block sidebar %}