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/UserManagement/UserManagement.module.css

@@ -4,22 +4,23 @@
   gap: 1px;
   background: var(--border-subtle);
   border: 1px solid var(--border-subtle);
-  border-radius: var(--radius-md);
+  border-radius: var(--radius-lg);
   min-height: 500px;
+  box-shadow: var(--shadow-card);
 }
 
 .listPane {
-  background: var(--bg-base);
+  background: var(--bg-surface);
   display: flex;
   flex-direction: column;
-  border-radius: var(--radius-md) 0 0 var(--radius-md);
+  border-radius: var(--radius-lg) 0 0 var(--radius-lg);
 }
 
 .detailPane {
-  background: var(--bg-base);
+  background: var(--bg-surface);
   overflow-y: auto;
   padding: 20px;
-  border-radius: 0 var(--radius-md) var(--radius-md) 0;
+  border-radius: 0 var(--radius-lg) var(--radius-lg) 0;
 }
 
 .listHeader {
@@ -180,3 +181,49 @@
 .providerBadge {
   margin-left: 6px;
 }
+
+.inherited {
+  opacity: 0.65;
+}
+
+.tabContent {
+  margin-top: 16px;
+}
+
+.emptySearch {
+  padding: 32px;
+  text-align: center;
+  color: var(--text-faint);
+  font-size: 12px;
+  font-family: var(--font-body);
+}
+
+.securitySection {
+  margin-top: 8px;
+  margin-bottom: 8px;
+}
+
+.securityRow {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+  font-size: 12px;
+  font-family: var(--font-body);
+  color: var(--text-primary);
+}
+
+.passwordDots {
+  font-family: var(--font-mono);
+  letter-spacing: 2px;
+}
+
+.resetForm {
+  display: flex;
+  gap: 8px;
+  align-items: center;
+  margin-top: 8px;
+}
+
+.resetInput {
+  width: 200px;
+}