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/static/js/stegasoo.js

@@ -765,18 +765,43 @@ const Stegasoo = {
         const customInputId = config.customInputId || 'channelCustomInput';
         const keyInputId = config.keyInputId || 'channelKeyInput';
         const generateBtnId = config.generateBtnId;
+        const serverInfoId = config.serverInfoId || 'channelServerInfo';
 
         const select = document.getElementById(selectId);
         const customInput = document.getElementById(customInputId);
         const keyInput = document.getElementById(keyInputId);
         const generateBtn = generateBtnId ? document.getElementById(generateBtnId) : null;
+        const serverInfo = document.getElementById(serverInfoId);
 
-        // Show/hide custom input based on selection
+        // Show/hide custom input and server info based on selection
         const updateVisibility = () => {
-            const isCustom = select?.value === 'custom';
+            const value = select?.value;
+            const isCustom = value === 'custom';
+            const isPublic = value === 'none';
+            const isAuto = value === 'auto';
+
+            // Custom input visibility
             customInput?.classList.toggle('d-none', !isCustom);
             if (isCustom && keyInput) {
                 keyInput.focus();
+                // Pulse highlight effect
+                customInput?.classList.add('channel-highlight');
+                setTimeout(() => customInput?.classList.remove('channel-highlight'), 400);
+            }
+
+            // Server info: show for auto, hide for custom, show "no key" for public
+            if (serverInfo) {
+                if (isAuto) {
+                    serverInfo.innerHTML = '<i class="bi bi-shield-lock me-1"></i>Server: <code>' + (serverInfo.dataset.fingerprint || '••••-••••-···-••••-••••') + '</code>';
+                    serverInfo.className = 'small text-success mt-2';
+                    serverInfo.classList.remove('d-none');
+                } else if (isPublic) {
+                    serverInfo.innerHTML = '<i class="bi bi-globe me-1"></i>No channel key will be used';
+                    serverInfo.className = 'small text-muted mt-2';
+                    serverInfo.classList.remove('d-none');
+                } else {
+                    serverInfo.classList.add('d-none');
+                }
             }
         };
 
@@ -912,7 +937,8 @@ const Stegasoo = {
         this.initChannelKey({
             selectId: 'channelSelectDec',
             customInputId: 'channelCustomInputDec',
-            keyInputId: 'channelKeyInputDec'
+            keyInputId: 'channelKeyInputDec',
+            serverInfoId: 'channelServerInfoDec'
         });
 
         // Form submission with channel key validation and mode display

frontends/web/static/style.css

@@ -161,6 +161,17 @@ body {
 .btn-group .btn-outline-secondary:hover {
     background-color: rgba(255, 255, 255, 0.08);
 }
+
+/* Channel key highlight pulse */
+.channel-highlight {
+    animation: channel-pulse 0.4s ease;
+}
+@keyframes channel-pulse {
+    0% { box-shadow: 0 0 0 0 rgba(254, 232, 98, 0); }
+    20% { box-shadow: 0 0 9px 1px rgba(254, 232, 98, 0.19); }
+    40% { box-shadow: 0 0 9px 1px rgba(254, 232, 98, 0.19); }
+    100% { box-shadow: 0 0 0 0 rgba(254, 232, 98, 0); }
+}
 .btn-group .btn-outline-primary:first-of-type,
 .btn-group .btn-outline-secondary:first-of-type {
     color: #6b4d8a;

frontends/web/templates/decode.html

@@ -362,15 +362,15 @@
                             </select>
 
                             <!-- Server channel indicator (compact) -->
+                            <div class="small text-success mt-2 {% if not channel_configured %}d-none{% endif %}" id="channelServerInfoDec" data-fingerprint="{{ channel_fingerprint[:4] }}-••••-···-••••-{{ channel_fingerprint[-4:] if channel_fingerprint else '' }}">
                                 {% if channel_configured %}
-                            <div class="small text-success mt-2">
                                 <i class="bi bi-shield-lock me-1"></i>
                                 Server: <code>{{ channel_fingerprint[:4] }}-••••-···-••••-{{ channel_fingerprint[-4:] }}</code>
-                            </div>
                                 {% endif %}
                             </div>
                           </div>
                         </div>
+                    </div>
 
                     <!-- Custom Channel Key Input (shown when Custom selected) -->
                     <div class="mb-4 d-none" id="channelCustomInputDec">

frontends/web/templates/encode.html

@@ -429,15 +429,15 @@
                             </select>
 
                             <!-- Server channel indicator (compact) -->
+                            <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 %}
-                            <div class="small text-success mt-2" id="channelServerInfo">
                                 <i class="bi bi-shield-lock me-1"></i>
                                 Server: <code>{{ channel_fingerprint[:4] }}-••••-···-••••-{{ channel_fingerprint[-4:] }}</code>
-                            </div>
                                 {% endif %}
                             </div>
                           </div>
                         </div>
+                    </div>
 
                     <!-- Custom Channel Key Input (shown when Custom selected) -->
                     <div class="mb-4 d-none" id="channelCustomInput">