feat: choose which probes link to which agents from the admin

The panel decides the probe/agent pairs and probes always dial out. A new
fleet.auto_link setting connects every probe to every agent (default); with it
off only the pairs chosen by hand connect, and any pair can be forced on or
off. The Probes page has a link matrix with the switch and per-pair toggles.

web/shared/api/client.ts

@@ -83,5 +83,6 @@ export const api = {
   get: <T>(path: string, query?: Query, init?: RequestInit) => request<T>('GET', withQuery(path, query), undefined, init),
   post: <T>(path: string, body?: unknown) => request<T>('POST', path, body ?? {}),
   patch: <T>(path: string, body: unknown) => request<T>('PATCH', path, body),
+  put: <T>(path: string, body: unknown) => request<T>('PUT', path, body),
   del: <T>(path: string) => request<T>('DELETE', path),
 }