feat(templates): add Vite Shadcn starter template

Introduce a new starter template for Vite with shadcn/ui integration. The template includes React, TypeScript, and Tailwind, and is added to the STARTER_TEMPLATES list. Additionally, update the styling in StarterTemplates component to better accommodate the new template and add the shadcn.svg icon.

icons/shadcn.svg

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg id="Layer_1" xmlns="http://www.w3.org/2000/svg" version="1.1" viewBox="0 0 256 256">
+  <!-- Generator: Adobe Illustrator 29.0.1, SVG Export Plug-In . SVG Version: 2.1.0 Build 192)  -->
+  <defs>
+    <style>
+      .st0, .st1 {
+        fill: none;
+      }
+
+      .st1 {
+        stroke: #7B7B7B; /* Changed from #000 to #7B7B7B */
+        stroke-linecap: round;
+        stroke-linejoin: round;
+        stroke-width: 32px;
+      }
+    </style>
+  </defs>
+  <rect class="st0" width="256" height="256"/>
+  <line class="st1" x1="208" y1="128" x2="128" y2="208"/>
+  <line class="st1" x1="192" y1="40" x2="40" y2="192"/>
+</svg>