feat: employee management — add/delete users from Members page

- Backend: POST /api/auth/users (create user), DELETE /api/auth/users/:id (delete user, unassign tasks)
- Frontend API: apiCreateUser, apiDeleteUser
- MembersPage: working Add Employee modal (name/email/password/role/dept), delete button with confirmation
- Only CEO/CTO/Manager roles see management controls
- CSS: btn-danger, btn-danger-sm styles

src/index.css

@@ -1655,7 +1655,44 @@ body {
   background: var(--accent-hover);
 }
 
-/* DEPENDENCIES */
+.btn-primary:disabled,
+.btn-danger:disabled {
+  opacity: 0.5;
+  cursor: not-allowed;
+}
+
+.btn-danger {
+  padding: 8px 18px;
+  background: #ef4444;
+  border: none;
+  border-radius: 8px;
+  color: #fff;
+  font-size: 13px;
+  font-weight: 700;
+  cursor: pointer;
+  font-family: inherit;
+  transition: background 0.15s;
+}
+
+.btn-danger:hover {
+  background: #dc2626;
+}
+
+.btn-danger-sm {
+  padding: 4px 8px;
+  background: rgba(239, 68, 68, 0.12);
+  border: 1px solid rgba(239, 68, 68, 0.25);
+  border-radius: 6px;
+  color: #ef4444;
+  font-size: 13px;
+  cursor: pointer;
+  transition: all 0.15s;
+}
+
+.btn-danger-sm:hover {
+  background: rgba(239, 68, 68, 0.25);
+  border-color: #ef4444;
+}
 .dep-unresolved-badge {
   background: rgba(239, 68, 68, 0.15);
   color: #ef4444;