fix: clean up account access grid and separate OIDC fields in user form

Use CSS grid for uniform account checkbox layout and add a bordered
subsection with heading for the OIDC identity fields.

public/css/style.css

@@ -867,19 +867,41 @@ input[type="file"] {
 }
 
 /* ── User management ── */
-.account-checkboxes { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 4px; }
+.account-checkboxes {
+  display: grid;
+  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
+  gap: 6px;
+  margin-top: 4px;
+}
 .account-checkbox-label {
   display: flex;
   align-items: center;
-  gap: 5px;
+  gap: 6px;
   font-size: 12px;
   background: var(--bg);
   border: 1px solid var(--border);
-  border-radius: 4px;
-  padding: 3px 8px;
+  border-radius: 6px;
+  padding: 6px 10px;
   cursor: pointer;
+  min-height: 34px;
 }
 .account-checkbox-label:hover { border-color: var(--primary); }
+.account-checkbox-label select {
+  margin-left: auto;
+  flex-shrink: 0;
+}
+
+.uf-oidc-section {
+  margin-top: 16px;
+  padding-top: 16px;
+  border-top: 1px solid var(--border);
+}
+.uf-oidc-section h4 {
+  font-size: 13px;
+  font-weight: 600;
+  margin-bottom: 10px;
+  color: var(--text-muted);
+}
 
 /* Hide layout editor button on portrait/mobile — canvas needs landscape space */
 @media (max-width: 768px), (orientation: portrait) {

public/index.html

@@ -149,7 +149,9 @@
               <label>Account Access <span class="field-hint">(admins see all — no selection needed)</span></label>
               <div id="uf-accounts-checkboxes" class="account-checkboxes"></div>
             </div>
-            <div id="uf-oidc-group" class="form-row" hidden>
+            <div id="uf-oidc-group" class="uf-oidc-section" hidden>
+              <h4>Single Sign-On Identity</h4>
+              <div class="form-row">
                 <div class="form-group">
                   <label for="uf-oidc-sub">OIDC Subject <span class="field-hint">(sub claim from provider)</span></label>
                   <input type="text" id="uf-oidc-sub" autocomplete="off">
@@ -159,6 +161,7 @@
                   <input type="text" id="uf-oidc-issuer" autocomplete="off">
                 </div>
               </div>
+            </div>
             <div id="user-form-error" class="wizard-error" hidden></div>
             <div style="display:flex;gap:8px;margin-top:12px">
               <button id="btn-save-user" class="btn-primary">Add User</button>