Add tutorial descriptions

Author: nikoscham

feascript-website.css

@@ -377,6 +377,13 @@ mjx-container {
   margin-bottom: 2px;
 }
 
+.tutorial-description {
+  font-size: 0.875em;
+  color: #666;
+  margin: 3px 0 0 0;
+  line-height: 1.4;
+}
+
 .tutorials-list .badge {
   display: inline-flex;
   align-items: center;

index.html

@@ -357,7 +357,7 @@ <h2 id="howtousefeascript"><a name="Getting Started"></a>How to Use FEAScript</h
       </p>
       <a href="https://codepen.io/FEAScript/pen/ByzVveQ" class="btn-codepen" target="_blank" rel="noopener">
         <svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><polygon points="5 3 19 12 5 21 5 3"></polygon></svg>
-        Run it on CodePen
+        Run it on CodePen<img src="https://upload.wikimedia.org/wikipedia/commons/4/44/Icon_External_Link.svg" alt="External Link Icon" style="width: 16px; height: 16px; vertical-align: middle; margin-left: 2px; margin-bottom: 4px" />
       </a>
     </div>
 
@@ -579,6 +579,7 @@ <h2 id="tutorials"><a name="Tutorials"></a>Tutorials</h2>
       <li>
         <div class="tutorial-card-content">
           <span class="tutorial-name">Advection-Diffusion with Gaussian Source</span>
+          <p class="tutorial-description"><em>1D steady-state scalar transport governed by the advection-diffusion equation with a localized Gaussian source term</em></p>
           <div class="tutorial-card-badges">
             <a href="https://feascript.com/tutorials/advection-diffusion-1d.html" class="badge badge-basic"
               >Basic HTML</a
@@ -609,6 +610,7 @@ <h2 id="tutorials"><a name="Tutorials"></a>Tutorials</h2>
       <li>
         <div class="tutorial-card-content">
           <span class="tutorial-name">Heat Conduction in a 2D Fin</span>
+          <p class="tutorial-description"><em>2D steady-state heat conduction in a cooling fin with mixed boundary conditions including constant temperature, symmetry, and convective cooling</em></p>
           <div class="tutorial-card-badges">
             <a href="https://feascript.com/tutorials/heat-conduction-2d-fin.html" class="badge badge-basic"
               >Basic HTML</a
@@ -650,6 +652,7 @@ <h2 id="tutorials"><a name="Tutorials"></a>Tutorials</h2>
       <li>
         <div class="tutorial-card-content">
           <span class="tutorial-name">Heat Conduction Through a Wall</span>
+          <p class="tutorial-description"><em>1D steady-state heat conduction across a wall with convection boundary condition at one end and constant temperature at the other</em></p>
           <div class="tutorial-card-badges">
             <a href="https://feascript.com/tutorials/heat-conduction-1d-wall.html" class="badge badge-basic"
               >Basic HTML</a
@@ -683,6 +686,7 @@ <h2 id="tutorials"><a name="Tutorials"></a>Tutorials</h2>
       <li>
         <div class="tutorial-card-content">
           <span class="tutorial-name">Creeping Flow on a Lid-Driven 2D Cavity</span>
+          <p class="tutorial-description"><em>Stokes flow in a square 2D cavity driven by a moving lid, with velocity and pressure fields resolved</em></p>
           <div class="tutorial-card-badges">
             <a
               href="https://feascript.com/tutorials/lid-driven-cavity-2d-creeping-flow.html"
@@ -712,6 +716,7 @@ <h2 id="tutorials"><a name="Tutorials"></a>Tutorials</h2>
       <li>
         <div class="tutorial-card-content">
           <span class="tutorial-name">Solidification Front Propagation in a 2D Domain</span>
+          <p class="tutorial-description"><em>Transient simulation of a solidification front advancing through a 2D domain using the eikonal equation</em></p>
           <div class="tutorial-card-badges">
             <a href="https://feascript.com/tutorials/solidification-front-2d.html" class="badge badge-basic"
               >Basic HTML</a