fix: variable blocks no longer emit labels; remove default array variable

- WCBlock.generateCode checks _isFlowBlock (set from #draw-area presence)
  before emitting labels/gotos; variable blocks in #variable-area skip this
- Remove unconditional vertices array creation in main() — it was only
  relevant for the SDL3 triangle template, which should create it itself
  if needed

app.js

@@ -430,16 +430,6 @@ function main() {
   prog.build();
   createDefaultMeasurements();
 
-  /* Create default vertex array for Hello Triangle */
-  const arr = prog.newArrayNode();
-  if (arr) {
-    arr.restoreData({
-      name: "vertices",
-      type: "float",
-      values: ["-0.5", "-0.5", "0.0", "0.5", "-0.5", "0.0", "0.0", "0.5", "0.0"]
-    });
-  }
-
   /* Load library index and create tabs (procedures load on demand) */
   initLibraries().then(() => {
     if (localStorage.getItem(STORAGE_KEY)) {

wcblock.js

@@ -45,7 +45,8 @@ class WCBlock extends HTMLElement {
       this._select();
     });
 
-    const isAlgoBlock = !!this.closest("#draw-area");
+    this._isFlowBlock = !!this.closest("#draw-area");
+    const isAlgoBlock = this._isFlowBlock;
     if (!(this instanceof WCStart) && !(this instanceof WCEnd) && !this.dataset.readonly) {
       const btn = document.createElement("button");
       btn.className = "delete-btn";
@@ -253,6 +254,7 @@ class WCBlock extends HTMLElement {
    * @returns {string}
    */
   generateCode(visited = new Set()) {
+    if (!this._isFlowBlock) return this.generateOwnCode();
     if (visited.has(this)) return "\n  goto " + this.id + ";\n";
     visited.add(this);
     return "\n" + this.id + ":\n" + this.generateOwnCode() + this.generateNextCode(visited);