feat: add user management modal with SSO/Local badges and fix OIDC session serialization

public/index.html

@@ -339,6 +339,7 @@
             </button>
           </div>
         </div>
+
         <div class="series-content">
           <div id="series-grid" class="series-grid">
             <div class="empty-state">
@@ -710,6 +711,7 @@
                   <thead>
                     <tr>
                       <th>Username</th>
+                      <th>Email</th>
                       <th>Role</th>
                       <th>Created</th>
                       <th>Actions</th>
@@ -976,6 +978,57 @@
       </svg> Hide</button>
   </div>
 
+  <!-- Edit User Modal -->
+  <div class="modal-overlay" id="edit-user-modal">
+    <div class="modal">
+      <div class="modal-header">
+        <h3 class="modal-title">Edit User</h3>
+        <button class="modal-close" id="edit-user-close">&times;</button>
+      </div>
+      <div class="modal-body">
+        <form id="edit-user-form">
+          <input type="hidden" id="edit-user-id">
+
+          <div class="modal-form-group">
+            <label for="edit-username">Username</label>
+            <input type="text" id="edit-username" name="username" class="form-input" required>
+          </div>
+
+          <div class="modal-form-group">
+            <label for="edit-email">Email</label>
+            <input type="text" id="edit-email" class="form-input" readonly disabled placeholder="No email associated">
+          </div>
+
+          <div class="modal-form-group">
+            <label for="edit-role">Role</label>
+            <select id="edit-role" name="role" class="form-input" required>
+              <option value="viewer">Viewer</option>
+              <option value="admin">Admin</option>
+            </select>
+          </div>
+
+          <div class="modal-form-group">
+            <label for="edit-password">New Password</label>
+            <input type="password" id="edit-password" name="password" class="form-input"
+              placeholder="Leave blank to keep current">
+            <p class="hint" id="edit-password-hint" style="margin-top: 4px;">Optional. Leave blank to keep unchanged.
+            </p>
+          </div>
+
+          <div class="modal-form-group hidden" id="oidc-info-group">
+            <label>OIDC Provider ID</label>
+            <code id="edit-oidc-id"
+              style="font-size: 0.8rem; color: var(--color-text-muted); padding: 4px; background: rgba(0,0,0,0.3); border-radius: 4px; display: block;"></code>
+          </div>
+        </form>
+      </div>
+      <div class="modal-footer">
+        <button class="btn btn-ghost" id="edit-user-cancel">Cancel</button>
+        <button class="btn btn-primary" id="edit-user-save">Save Changes</button>
+      </div>
+    </div>
+  </div>
+
   <!-- JavaScript -->
   <script src="/js/icons.js"></script>
   <script src="/js/api.js?v=2"></script>