Update Open Source Stack copy and fix contact email

- Rename "Open Source Software" → "Open Source Stack" across site; reframe
  as fully open hardware-to-GUI stack (PCB schematics, CAD, firmware, AI,
  GUI all free and open)
- Fix contact email to bournemouthtech@protonmail.com (was typo'd with extra
  syllable in previous commit)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

devkits.html

@@ -136,7 +136,7 @@
               2.4GHz radio antenna
             </li>
           </ul>
-          <a href="mailto:bournemouththechnology@protonmail.com" class="btn btn-dark btn-md" style="margin-top:auto;">Buy now</a>
+          <a href="mailto:bournemouthtech@protonmail.com" class="btn btn-dark btn-md" style="margin-top:auto;">Buy now</a>
         </div>
 
         <!-- Edge Compute Kit (featured) -->
@@ -170,7 +170,7 @@
               Thermal management system
             </li>
           </ul>
-          <a href="mailto:bournemouththechnology@protonmail.com" class="btn btn-white btn-md" style="margin-top:auto;">Buy now</a>
+          <a href="mailto:bournemouthtech@protonmail.com" class="btn btn-white btn-md" style="margin-top:auto;">Buy now</a>
         </div>
 
         <!-- Heavy Lift -->
@@ -197,7 +197,7 @@
               Custom consultancy included
             </li>
           </ul>
-          <a href="mailto:bournemouththechnology@protonmail.com" class="btn btn-outline btn-md" style="margin-top:auto;">Get in touch</a>
+          <a href="mailto:bournemouthtech@protonmail.com" class="btn btn-outline btn-md" style="margin-top:auto;">Get in touch</a>
         </div>
 
       </div>
@@ -211,7 +211,7 @@
         </div>
         <div style="display:flex;align-items:center;justify-content:flex-end;gap:20px;flex-wrap:wrap;">
           <div class="product-price" style="font-size:18px;color:var(--ink-3);">Contact for pricing</div>
-          <a href="mailto:bournemouththechnology@protonmail.com" class="btn btn-outline btn-md">Get in touch</a>
+          <a href="mailto:bournemouthtech@protonmail.com" class="btn btn-outline btn-md">Get in touch</a>
         </div>
       </div>