Remove Discord, fix email, wire YouTube, drop community sections

- Remove all Discord references across every page
- Fix email to bournemouththechnology@protonmail.com throughout
- Wire YouTube footer links to @JonStarkeyfilms channel
- Replace Discord hero link on index with YouTube
- Remove "Built by builders" + "Join the community" section (devkits)
- Remove Discord Server item from opensource community list

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

videos.html

@@ -342,9 +342,8 @@
         <div>
           <div class="footer-col-label">Connect</div>
           <div class="footer-col-links">
-            <a href="opensource.html">Discord</a>
             <a href="consultancy.html">Contact</a>
-            <a href="videos.html">YouTube</a>
+            <a href="https://www.youtube.com/@JonStarkeyfilms">YouTube</a>
           </div>
         </div>
       </div>