maker: pan dell'immagine di prova non si interrompe col mouse (Refs #104)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Jbf7qKuxsnAVjxthRy7dnB

src/frontend/flask_app/static/js/dxf_recipe_wizard.js

@@ -430,6 +430,8 @@ function dxfRecipeWizard(taskId, csrf, msgs) {
     onPanDown(ev) {
       const vp = this.$refs.viewport;
       if (!vp || (ev.pointerType === 'mouse' && ev.button)) return;
+      // #104: senza preventDefault Chromium manda pointercancel al primo movimento del mouse e il pan si ferma
+      if (ev.preventDefault) ev.preventDefault();
       this._pan = { x: ev.clientX, y: ev.clientY, left: vp.scrollLeft, top: vp.scrollTop };
       this.panning = true;
       try { vp.setPointerCapture(ev.pointerId); } catch (e) { /* puntatore gia' rilasciato */ }