feat: open webhook response (HTML/PDF) in new window, update success text

- Replace fetch() with hidden form POST + target='_blank' so the webhook's
  auto-download HTML page opens in a new tab/window
- Send form-encoded fields (not JSON) since webhook expects POST form data
- Update success message: 'A new window has opened with your personalized
  Odoo project plan. The download will start automatically after research
  is complete.'
- Remove dead bizDownloadBtn references (button no longer needed)

index.html

@@ -418,8 +418,7 @@
         <div class="biz-success" id="bizSuccess" style="display:none">
           <i class="fas fa-check-circle"></i>
           <h3>Your project plan is being prepared</h3>
-          <p>Download your personalized PDF below — a custom Odoo implementation roadmap tailored to your business.</p>
-          <a class="btn btn-brass btn-lg" id="bizDownloadBtn" style="display:none" download>Download Your Project Plan &darr;</a>
+          <p>A new window has opened with your personalized Odoo project plan. The download will start automatically after research is complete.</p>
         </div>
       </div>
     </section>