feat: harmonize admin pages to split-pane layout with shared CSS

Extract shared admin layout styles into AdminLayout.module.css and
convert all admin pages to consistent patterns: Database/OpenSearch/
Audit Log use split-pane master/detail, OIDC uses full-width detail-only
with unified panelHeader treatment across all pages.

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

ui/src/pages/admin/OidcAdminPage.module.css

@@ -1,29 +1,4 @@
-.page {
-  max-width: 640px;
-  margin: 0 auto;
-  padding: 32px 16px;
-}
-
-.pageTitle {
-  font-size: 20px;
-  font-weight: 600;
-  color: var(--text-primary);
-  margin-bottom: 4px;
-}
-
-.subtitle {
-  font-size: 13px;
-  color: var(--text-muted);
-  margin-bottom: 24px;
-}
-
-.card {
-  background: var(--bg-surface);
-  border: 1px solid var(--border-subtle);
-  border-radius: var(--radius-lg);
-  padding: 32px;
-}
-
+/* ─── Toggle ─── */
 .toggleRow {
   display: flex;
   align-items: flex-start;
@@ -84,6 +59,7 @@
   background: #0a0e17;
 }
 
+/* ─── Form Fields ─── */
 .field {
   margin-top: 16px;
 }
@@ -123,6 +99,7 @@
   box-shadow: 0 0 0 3px var(--amber-glow);
 }
 
+/* ─── Tags ─── */
 .tags {
   display: flex;
   flex-wrap: wrap;
@@ -182,31 +159,17 @@
   color: var(--text-primary);
 }
 
-.actions {
-  display: flex;
-  align-items: center;
-  gap: 12px;
-  margin-top: 24px;
-  padding-top: 20px;
-  border-top: 1px solid var(--border-subtle);
-}
-
+/* ─── Header Action Button Variants ─── */
 .btnPrimary {
-  padding: 10px 24px;
-  border-radius: var(--radius-sm);
-  border: 1px solid var(--amber);
-  background: var(--amber);
-  color: #0a0e17;
-  font-family: var(--font-body);
-  font-size: 14px;
+  border-color: var(--amber) !important;
+  background: var(--amber) !important;
+  color: #0a0e17 !important;
   font-weight: 600;
-  cursor: pointer;
-  transition: all 0.15s;
 }
 
-.btnPrimary:hover {
-  background: var(--amber-hover);
-  border-color: var(--amber-hover);
+.btnPrimary:hover:not(:disabled) {
+  background: var(--amber-hover) !important;
+  border-color: var(--amber-hover) !important;
 }
 
 .btnPrimary:disabled {
@@ -215,19 +178,12 @@
 }
 
 .btnOutline {
-  padding: 10px 24px;
-  border-radius: var(--radius-sm);
   background: transparent;
-  border: 1px solid var(--border);
+  border-color: var(--border);
   color: var(--text-secondary);
-  font-family: var(--font-body);
-  font-size: 14px;
-  font-weight: 500;
-  cursor: pointer;
-  transition: all 0.15s;
 }
 
-.btnOutline:hover {
+.btnOutline:hover:not(:disabled) {
   border-color: var(--amber-dim);
   color: var(--text-primary);
 }
@@ -238,21 +194,13 @@
 }
 
 .btnDanger {
-  margin-left: auto;
-  padding: 10px 24px;
-  border-radius: var(--radius-sm);
-  background: transparent;
-  border: 1px solid var(--rose-dim);
-  color: var(--rose);
-  font-family: var(--font-body);
-  font-size: 14px;
-  font-weight: 500;
-  cursor: pointer;
-  transition: all 0.15s;
+  border-color: var(--rose-dim) !important;
+  color: var(--rose) !important;
+  background: transparent !important;
 }
 
-.btnDanger:hover {
-  background: var(--rose-glow);
+.btnDanger:hover:not(:disabled) {
+  background: var(--rose-glow) !important;
 }
 
 .btnDanger:disabled {
@@ -260,6 +208,7 @@
   cursor: not-allowed;
 }
 
+/* ─── Confirm Bar ─── */
 .confirmBar {
   display: flex;
   align-items: center;
@@ -283,6 +232,7 @@
   gap: 8px;
 }
 
+/* ─── Status Messages ─── */
 .successMsg {
   margin-top: 16px;
   padding: 10px 12px;
@@ -303,6 +253,7 @@
   color: var(--rose);
 }
 
+/* ─── Skeleton Loading ─── */
 .skeleton {
   animation: pulse 1.5s ease-in-out infinite;
   background: var(--bg-raised);
@@ -322,13 +273,6 @@
   width: 60%;
 }
 
-.accessDenied {
-  text-align: center;
-  padding: 64px 16px;
-  color: var(--text-muted);
-  font-size: 14px;
-}
-
 @keyframes pulse {
   0%, 100% { opacity: 0.4; }
   50% { opacity: 0.8; }