refactor: replace native HTML with design system components (Phase 5)

- EnvironmentSelector: bare <select> -> DS Select
- LogTab: raw <table> + <input> + <button> -> DS LogViewer + Input + Button
- AppsTab: 3 homegrown sub-tab bars -> DS Tabs, remove unused CSS
- AppConfigDetailPage: 4x <select> -> DS Select, 2x <input checkbox> ->
  DS Toggle, 7x <label> -> DS Label, 4x <button> -> DS Button
- AgentHealth: 4x <select> -> DS Select, 7x <button> -> DS Button

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

ui/src/pages/Admin/AppConfigDetailPage.module.css

@@ -17,71 +17,12 @@
   margin-bottom: 20px;
 }
 
-.backBtn {
-  background: none;
-  border: none;
-  color: var(--amber);
-  cursor: pointer;
-  font-size: 13px;
-  font-weight: 500;
-  padding: 4px 0;
-}
-
-.backBtn:hover {
-  color: var(--amber-deep);
-  text-decoration: underline;
-}
-
 .toolbarActions {
   display: flex;
   gap: 8px;
   align-items: center;
 }
 
-.editBtn {
-  background: none;
-  border: 1px solid var(--border-subtle);
-  border-radius: var(--radius-sm);
-  color: var(--text-secondary);
-  cursor: pointer;
-  font-size: 12px;
-  padding: 5px 12px;
-}
-
-.editBtn:hover {
-  border-color: var(--amber);
-  color: var(--amber);
-}
-
-.cancelBtn {
-  background: none;
-  border: 1px solid var(--border-subtle);
-  border-radius: var(--radius-sm);
-  color: var(--text-muted);
-  cursor: pointer;
-  font-size: 12px;
-  padding: 5px 12px;
-}
-
-.cancelBtn:hover {
-  border-color: var(--text-faint);
-  color: var(--text-primary);
-}
-
-.removeBtn {
-  background: none;
-  border: none;
-  color: var(--text-faint);
-  cursor: pointer;
-  font-size: 16px;
-  padding: 0 4px;
-  line-height: 1;
-}
-
-.removeBtn:hover {
-  color: var(--error);
-}
-
 .header {
   margin-bottom: 16px;
   background: var(--bg-surface);
@@ -122,13 +63,7 @@
   min-width: 140px;
 }
 
-.label {
-  font-size: 12px;
-  font-weight: 600;
-  color: var(--text-secondary);
-}
-
-.select {
+.numberInput {
   padding: 6px 10px;
   border: 1px solid var(--border-subtle);
   border-radius: var(--radius-sm);
@@ -140,24 +75,10 @@
   max-width: 360px;
 }
 
-.select:focus {
+.numberInput:focus {
   border-color: var(--amber);
 }
 
-.toggleRow {
-  display: flex;
-  align-items: center;
-  gap: 8px;
-  font-size: 13px;
-  color: var(--text-secondary);
-  cursor: pointer;
-}
-
-.toggleRow input {
-  accent-color: var(--amber);
-  cursor: pointer;
-}
-
 .tapBadges {
   display: flex;
   flex-wrap: wrap;