feat(webui): MCP & Agents admin tab

New 'MCP & Agents' tab (after Charts) fed by GET /admin/api/targets:
two Card panels, each a sortable DataTable (reusing DataTable/
SortHeaderButton — no hand-rolled table markup) listing configured
MCP servers and agents with name, url (muted, truncated with a title
tooltip), access (Badge per allowed group, muted 'All groups' when
unrestricted — the same idiom UsageView's own group Access block
already uses), and req/min, req/day, req/month.

- types/api.ts: AdminTargetCountersView/AdminTargetView/
  AdminTargetsResponse matching admin.go's JSON exactly.
- stores/dashboard.ts: targets fetched in the SAME Promise.all/5s
  poll as overview and usage — one store, one timer, not a third.
- lib/target-columns.ts: shared ColumnDef set both DataTables use.
- components/TargetsView.vue: SearchInput + useSearchQuery name
  filter (inline matching, mirroring ProvidersView's own single-field
  aliasMatches — not every filter needs a lib/*-search.ts module).

webui/src/App.vue

@@ -5,6 +5,7 @@ import { computed, defineAsyncComponent, onMounted, ref } from 'vue'
 
 import AuthGate from '@/components/AuthGate.vue'
 import ProvidersView from '@/components/ProvidersView.vue'
+import TargetsView from '@/components/TargetsView.vue'
 import { Button } from '@/components/ui/button'
 import { Tabs, TabsContent, TabsList, TabsTrigger } from '@/components/ui/tabs'
 import UsageView from '@/components/UsageView.vue'
@@ -28,7 +29,7 @@ const dashboard = useDashboardStore()
 // fetches from, GET /admin/api/overview, and the store's own `overview`
 // field (AdminOverviewResponse) keep their original names unchanged — the
 // rename is UI-only, not an API surface change.
-const activeView = ref<'providers' | 'usage' | 'charts'>('providers')
+const activeView = ref<'providers' | 'usage' | 'charts' | 'targets'>('providers')
 
 const statusText = computed<string>(() => {
   if (dashboard.error) return `refresh failed: ${dashboard.error}`
@@ -72,6 +73,7 @@ onMounted(() => {
         <TabsTrigger value="providers">Providers</TabsTrigger>
         <TabsTrigger value="usage">Usage</TabsTrigger>
         <TabsTrigger value="charts">Charts</TabsTrigger>
+        <TabsTrigger value="targets">MCP & Agents</TabsTrigger>
       </TabsList>
       <TabsContent value="providers">
         <ProvidersView />
@@ -82,6 +84,9 @@ onMounted(() => {
       <TabsContent value="charts">
         <ChartsView />
       </TabsContent>
+      <TabsContent value="targets">
+        <TargetsView />
+      </TabsContent>
     </Tabs>
   </div>
 </template>