feat: show loading spinner instead of static SVG placeholder on initial modal load

Author: ThisIs-Developer

script.js

@@ -6497,7 +6497,7 @@ document.addEventListener("DOMContentLoaded", async function () {
           <div style="display:flex; flex-direction:column; align-items:center; width:100%; height:100%;">
             <div style="font-size:10px; font-weight:${titleWeight}; color:${titleColor}; margin-bottom:4px;">${t.title}</div>
             <div class="diagram-svg-container diagram-svg-${catClass}" style="flex:1; width:100%; display:flex; align-items:center; justify-content:center; overflow:hidden;">
-              ${t.svg}
+              <div class="loading-spinner">Loading...</div>
             </div>
           </div>
         `;
@@ -6540,7 +6540,7 @@ document.addEventListener("DOMContentLoaded", async function () {
           // Render bottom preview container with API image & fallback
           previewContainer.innerHTML = `
             <div class="diagram-svg-container diagram-svg-${catClass}" style="width:100%; height:100%; display:flex; align-items:center; justify-content:center; overflow:hidden;">
-              ${t.svg}
+              <div class="loading-spinner">Loading...</div>
             </div>
           `;