Add dynamic channel selector feedback with pulse highlight

- Channel select shows contextual info: Auto (server key), Public (no key), Custom (hidden)
- Gold pulse highlight on custom channel input when selected
- Smooth 0.4s animation with subtle glow effect
- Updated encode.html and decode.html with data-fingerprint attributes

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontends/web/templates/encode.html

@@ -429,12 +429,12 @@
                             </select>
 
                             <!-- Server channel indicator (compact) -->
-                            {% if channel_configured %}
-                            <div class="small text-success mt-2" id="channelServerInfo">
+                            <div class="small text-success mt-2 {% if not channel_configured %}d-none{% endif %}" id="channelServerInfo" data-fingerprint="{{ channel_fingerprint[:4] }}-••••-···-••••-{{ channel_fingerprint[-4:] if channel_fingerprint else '' }}">
+                                {% if channel_configured %}
                                 <i class="bi bi-shield-lock me-1"></i>
                                 Server: <code>{{ channel_fingerprint[:4] }}-••••-···-••••-{{ channel_fingerprint[-4:] }}</code>
+                                {% endif %}
                             </div>
-                            {% endif %}
                           </div>
                         </div>
                     </div>