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/components/EnvironmentSelector.tsx

@@ -1,3 +1,5 @@
+import { useMemo } from 'react';
+import { Select } from '@cameleer/design-system';
 import styles from './EnvironmentSelector.module.css';
 
 interface EnvironmentSelectorProps {
@@ -9,17 +11,20 @@ interface EnvironmentSelectorProps {
 export function EnvironmentSelector({ environments, value, onChange }: EnvironmentSelectorProps) {
   if (environments.length === 0) return null;
 
+  const options = useMemo(
+    () => [
+      { value: '', label: 'All Envs' },
+      ...environments.map((env) => ({ value: env, label: env })),
+    ],
+    [environments],
+  );
+
   return (
-    <select
+    <Select
       className={styles.select}
+      options={options}
       value={value ?? ''}
       onChange={(e) => onChange(e.target.value || undefined)}
-      aria-label="Environment filter"
-    >
-      <option value="">All Envs</option>
-      {environments.map((env) => (
-        <option key={env} value={env}>{env}</option>
-      ))}
-    </select>
+    />
   );
 }