Fix ParseMultipartForm for SetUserAdmin endpoint

The SetUserAdmin endpoint was using ParseForm() which doesn't handle
multipart/form-data (what JavaScript FormData sends). This caused the
is_admin field to be empty/missing, defaulting to false.

Applied the same fix as SetDisplayName - try ParseMultipartForm first,
fall back to ParseForm.

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

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

src/main/go/net/eagle0/admin_server/admin_server.go

@@ -1712,12 +1712,20 @@ func handleSetUserDisplayName(w http.ResponseWriter, r *http.Request, userID str
 		return
 	}
 
-	if err := r.ParseForm(); err != nil {
-		http.Error(w, "Invalid form data", http.StatusBadRequest)
-		return
+	// Debug: log content type and try both parsing methods
+	contentType := r.Header.Get("Content-Type")
+	log.Printf("[Debug] SetDisplayName Content-Type: %s", contentType)
+
+	if err := r.ParseMultipartForm(32 << 20); err != nil {
+		log.Printf("[Debug] ParseMultipartForm error: %v, trying ParseForm", err)
+		if err := r.ParseForm(); err != nil {
+			http.Error(w, "Invalid form data", http.StatusBadRequest)
+			return
+		}
 	}
 
 	displayName := r.FormValue("display_name")
+	log.Printf("[Debug] Parsed display_name: %q, Form: %v, PostForm: %v", displayName, r.Form, r.PostForm)
 
 	ctx, cancel := createAdminContext(r)
 	defer cancel()
@@ -1753,12 +1761,18 @@ func handleSetUserAdmin(w http.ResponseWriter, r *http.Request, userID string) {
 		return
 	}
 
-	if err := r.ParseForm(); err != nil {
-		http.Error(w, "Invalid form data", http.StatusBadRequest)
-		return
+	// Parse multipart form (FormData from JavaScript sends multipart/form-data)
+	if err := r.ParseMultipartForm(32 << 20); err != nil {
+		// Fall back to regular form parsing for application/x-www-form-urlencoded
+		if err := r.ParseForm(); err != nil {
+			http.Error(w, "Invalid form data", http.StatusBadRequest)
+			return
+		}
 	}
 
-	isAdmin := r.FormValue("is_admin") == "true"
+	isAdminStr := r.FormValue("is_admin")
+	isAdmin := isAdminStr == "true"
+	log.Printf("[Debug] SetUserAdmin: is_admin=%q, parsed=%v", isAdminStr, isAdmin)
 
 	ctx, cancel := createAdminContext(r)
 	defer cancel()

src/main/go/net/eagle0/admin_server/templates/users.html

@@ -100,8 +100,8 @@
             <div id="edit-feedback"></div>
         </form>
         <footer>
-            <button class="secondary" onclick="document.getElementById('edit-modal').close()">Cancel</button>
-            <button onclick="saveUserChanges()">Save Changes</button>
+            <button type="button" class="secondary" onclick="document.getElementById('edit-modal').close()">Cancel</button>
+            <button type="button" onclick="saveUserChanges()">Save Changes</button>
         </footer>
     </article>
 </dialog>
@@ -124,6 +124,7 @@ function saveUserChanges() {
     const isAdmin = document.getElementById('edit-is-admin').checked;
     const feedback = document.getElementById('edit-feedback');
 
+    console.log('saveUserChanges called:', {userId, displayName, isAdmin, originalIsAdmin});
     feedback.innerHTML = '<p>Saving...</p>';
 
     // Update display name