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/lib/target-columns.ts

@@ -0,0 +1,74 @@
+import type { ColumnDef } from '@tanstack/vue-table'
+import { h } from 'vue'
+
+import { Badge } from '@/components/ui/badge'
+import type { AdminTargetView } from '@/types/api'
+
+/**
+ * numericColumn builds one right-aligned, sortable request-counter column.
+ * Mirrors usage-columns.ts's own helper of the same name and purpose, but
+ * without that one's storeDown '?' masking: a target's counters carry no
+ * storeDown flag (limiter.targetUsage, limits.go — a target scope has no
+ * limit to protect from a misleadingly-confident zero, unlike a limited
+ * user/group scope), so there is nothing to mask here.
+ */
+function numericColumn(id: string, header: string, read: (t: AdminTargetView) => number): ColumnDef<AdminTargetView, unknown> {
+  return {
+    id,
+    header,
+    accessorFn: read,
+    meta: { align: 'right' },
+    cell: ({ row }) => String(read(row.original)),
+  }
+}
+
+/**
+ * targetColumns builds the shared TanStack `ColumnDef` set both the MCP
+ * servers and the Agents DataTable in TargetsView.vue use (admin.go:
+ * adminTargetView — the two tables share one identical row shape). name is
+ * plain text (not the ModelChip copy treatment — a target name is not a
+ * routable model id); url is muted and truncated with a title attribute
+ * for the full value; access renders as a Badge per allowed group, or a
+ * muted "All groups" when unrestricted — the exact idiom UsageView.vue's
+ * own group Access block already established (Providers/Models/MCP
+ * servers/Agents dt/dd pairs there).
+ */
+export function targetColumns(): ColumnDef<AdminTargetView, unknown>[] {
+  return [
+    {
+      id: 'name',
+      header: 'Name',
+      accessorFn: (t) => t.name,
+      cell: ({ row }) => h('span', { class: 'font-medium' }, row.original.name),
+    },
+    {
+      id: 'url',
+      header: 'URL',
+      accessorFn: (t) => t.url,
+      cell: ({ row }) =>
+        h(
+          'span',
+          { class: 'block max-w-xs truncate text-muted-foreground', title: row.original.url },
+          row.original.url,
+        ),
+    },
+    {
+      id: 'access',
+      header: 'Access',
+      enableSorting: false,
+      accessorFn: (t) => (t.access ?? []).join(', '),
+      cell: ({ row }) => {
+        const access = row.original.access
+        if (!access?.length) return h('span', { class: 'text-muted-foreground' }, 'All groups')
+        return h(
+          'div',
+          { class: 'flex flex-wrap gap-1.5' },
+          access.map((name) => h(Badge, { key: name, as: 'span', variant: 'secondary', class: 'font-mono font-normal' }, () => name)),
+        )
+      },
+    },
+    numericColumn('reqMin', 'req/min', (t) => t.counters.requestsPerMinute),
+    numericColumn('reqDay', 'req/day', (t) => t.counters.requestsPerDay),
+    numericColumn('reqMonth', 'req/month', (t) => t.counters.requestsPerMonth),
+  ]
+}