feat: standardize navbar logo size

Introduced a specific height for the navbar logo across the application
to ensure consistency in the navbar's visual presentation. By adjusting
the CSS to set a fixed height and applying the corresponding class to
the logo in the header, the layout becomes more predictable and
harmonious, significantly improving the user interface's appearance.

static/css/style.css

@@ -205,3 +205,7 @@ header {
   word-wrap: break-word;
   overflow-wrap: break-word;
 }
+
+.navbar-logo {
+  height: 64px;
+}

templates/header.html

@@ -1,7 +1,7 @@
 <header>
   <nav class="navbar navbar-expand-lg navbar-light bg-light">
     <a class="navbar-brand" href="/">
-      <img src="/static/img/logo.png" alt="Structables" />
+      <img class="navbar-logo" src="/static/img/logo.png" alt="Structables" />
     </a>
     <div class="container-fluid">
       <div class="navbar-nav-scroll">