refactor: admin section UX/UI redesign

- Fix critical --bg-base token bug (dark mode broken), replace with --bg-surface
- Replace hand-rolled admin nav with Tabs composite (proper ARIA)
- Migrate AuditLog from custom table to DataTable with sorting, row accents, card wrapper
- Remove duplicate h2 page titles (breadcrumb + tab already identify the page)
- Rework user creation with provider-aware form (Local/OIDC RadioGroup)
- Add Security section with password reset for local users, OIDC info for external
- Add toast notifications to all RBAC mutations (create/delete/add/remove)
- Add confirmation dialogs for cascading removals (group/role)
- Add keyboard accessibility to entity lists (role/tabIndex/aria-selected)
- Add empty search states, duplicate name validation
- Replace lock emoji with Badge, fix radii/shadow/padding consistency
- Badge dashed variant keeps background color
- Inherited roles shown with dashed outline + reduced opacity
- Inline MultiSelect (+Add) for groups, roles, members, child groups
- Center OIDC form, replace inline styles with CSS modules

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/pages/Admin/OidcConfig/OidcConfig.module.css

@@ -1,25 +1,13 @@
 .page {
   max-width: 640px;
+  margin: 0 auto;
 }
 
-.header {
-  display: flex;
-  align-items: center;
-  justify-content: space-between;
-  margin-bottom: 20px;
-}
-
-.title {
-  font-size: 18px;
-  font-weight: 600;
-  color: var(--text-primary);
-  margin: 0;
-  font-family: var(--font-body);
-}
-
-.headerActions {
+.toolbar {
   display: flex;
   gap: 8px;
+  justify-content: flex-end;
+  margin-bottom: 20px;
 }
 
 .section {