feat: add invite code validity controls

- Add invite code starts/expires fields across contracts, API, Spacetime bindings, and admin UI
- Enforce pending/expired invite code redemption behavior and expose admin status
- Add admin write-operation confirmation guard and documentation
- Add invite code contract/runtime tests

apps/admin-web/src/styles/admin.css

@@ -457,6 +457,47 @@ button:disabled {
   font-weight: 700;
 }
 
+.admin-confirm-backdrop {
+  position: fixed;
+  inset: 0;
+  z-index: 80;
+  display: grid;
+  place-items: center;
+  background: rgba(23, 33, 43, 0.42);
+  padding: 16px;
+}
+
+.admin-confirm-panel {
+  display: grid;
+  width: min(100%, 420px);
+  gap: 16px;
+  border: 1px solid #d8e2e8;
+  border-radius: 10px;
+  background: #ffffff;
+  box-shadow: 0 22px 60px rgba(23, 33, 43, 0.24);
+  padding: 18px;
+}
+
+.admin-confirm-warning {
+  border: 1px solid #efc894;
+  border-radius: 8px;
+  color: #8a5a1b;
+  background: #fffaf3;
+  padding: 10px 12px;
+  font-size: 13px;
+  font-weight: 650;
+}
+
+.admin-confirm-actions {
+  display: flex;
+  justify-content: flex-end;
+  gap: 10px;
+}
+
+.admin-confirm-actions button {
+  min-width: 92px;
+}
+
 .admin-primary-button {
   color: #ffffff;
   background: #126e82;
@@ -575,6 +616,11 @@ button:disabled {
   background: #e6f5ed;
 }
 
+.admin-status-pending {
+  color: #8a5a1b;
+  background: #fff4df;
+}
+
 .admin-status-error {
   color: #8a2f2f;
   background: #fff1ef;
@@ -755,6 +801,14 @@ button:disabled {
     padding: 16px;
   }
 
+  .admin-confirm-panel {
+    padding: 16px;
+  }
+
+  .admin-confirm-actions {
+    display: grid;
+  }
+
   .admin-login-brand h1,
   .admin-page-heading h2 {
     font-size: 22px;