Fix dashboard token UX: token required for public space, preserve existing token on save

src/reachy_mini_remote_control_app/templates/dashboard.html

@@ -226,11 +226,12 @@
             </div>
 
             <div class="form-group">
-                <label for="hf-token">HuggingFace Token (for Private Spaces)</label>
+                <label for="hf-token">HuggingFace Token</label>
                 <input type="password" id="hf-token" placeholder="hf_...">
                 <p style="font-size: 12px; color: #666; margin-top: 5px;">
-                    Required only for private HuggingFace Spaces. Create a token with 'read' permissions at
-                    <a href="https://huggingface.co/settings/tokens" target="_blank" style="color: #667eea;">huggingface.co/settings/tokens</a>
+                    Required to authenticate your robot with the public or private space. Create a token with 'read' permissions at
+                    <a href="https://huggingface.co/settings/tokens" target="_blank" style="color: #667eea;">huggingface.co/settings/tokens</a>.
+                    Leave blank to keep the existing token.
                 </p>
             </div>
 
@@ -287,7 +288,7 @@
 
             <div style="margin-top: 20px; padding: 15px; background: rgba(16, 185, 129, 0.1); border-radius: 8px; border-left: 4px solid #10b981;">
                 <p style="margin: 0; color: #065f46; font-size: 14px;">
-                    <strong>Quick Start:</strong> Use the public shared space (no token required):
+                    <strong>Quick Start:</strong> Use the public shared space:
                     <code style="background: rgba(0,0,0,0.1); padding: 2px 6px; border-radius: 4px; margin-left: 8px;">wss://huggingfacem4-reachy-mini-remote-control.hf.space</code>
                 </p>
                 <button onclick="usePublicSpace()" style="background: #10b981; color: white; border: none; padding: 8px 16px; border-radius: 6px; cursor: pointer; font-size: 12px; margin-top: 10px; font-weight: 600;">
@@ -367,6 +368,7 @@
                 // Load HF token if present (don't display full token for security)
                 if (data.hf_token && data.hf_token.length > 0) {
                     document.getElementById('hf-token').placeholder = '••••••••' + data.hf_token.slice(-4);
+                    currentConfig.hf_token = data.hf_token;
                 }
 
                 // Set the dropdown to match current URI if it's one of the presets
@@ -405,9 +407,10 @@
                     METRICS_LOG_INTERVAL_SEC: '5'
                 };
 
-                // Only add HF_TOKEN if provided
-                if (hfToken && hfToken.trim().length > 0) {
-                    configData.HF_TOKEN = hfToken.trim();
+                // Use the provided token, or fall back to the existing token to avoid losing it
+                const tokenToSave = (hfToken && hfToken.trim().length > 0) ? hfToken.trim() : currentConfig.hf_token;
+                if (tokenToSave) {
+                    configData.HF_TOKEN = tokenToSave;
                 }
 
                 const response = await fetch('/profile/default/config', {