Resource subscribe/unsubscribe failures are silent — a bare `void` discards the promise

[cliffhall]

onSubscribeResource and onUnsubscribeResource discard their promise with a bare void, so a failed subscribe or unsubscribe is invisible to the user and surfaces as an unhandled browser rejection.

// clients/web/src/hooks/useServerCommands.tsx
const onSubscribeResource = useCallback(
  (uri: string) => {
    if (!inspectorClient) return;
    void inspectorClient.subscribeToResource(uri);
  },
  [inspectorClient],
);

The callee does not own its failures. InspectorClient.subscribeToResource throws on "Client is not connected", on "Server does not support resource subscriptions", and it rethrows a wrapped transport/request error after rolling its subscription state back. unsubscribeFromResource is the same shape. AGENTS.md states the rule this breaks directly:

Reach for [void] only when the callee already owns its failures … Where the callee does not own its failures, give it a catch rather than voiding the call.

Every neighbouring command in that hook already routes through the shared recovery — onCancelTask, onSetLogLevel, the refreshes and the load-mores all go through runWithCommandAuthRecovery / runCommandInBackground. These two are the only ones that do not, so a mid-session 401 on a subscribe does not trigger re-auth the way a 401 on a refresh does, and any other failure is silent.

Why it isn't fixed in #2173

Both lines were moved verbatim by #2155 (PR #2173), which is a decomposition step carrying an explicit "no behavior change" constraint — routing them through runCommandInBackground adds auth recovery and an error toast, which is a real behavior change and does not belong buried in a relocation. Raised by Copilot on that PR and deliberately deferred here.

Repro

1. Connect to subscriptions-legacy-http.json from test-servers/configs.
2. Subscribe to a resource, then kill the server (or let the session lapse).
3. Click Subscribe again — nothing happens in the UI; the rejection appears only in the browser console.

Proposed fix

Route both through runCommandInBackground(..., "resource", "Failed to subscribe to resource") so a 401 recovers like every other command and any other failure toasts. Cover both in useServerCommands.test.tsx — the harness already reproduces the wrapper's shape.

Done when

• Neither handler discards its promise
• A mid-session 401 on subscribe/unsubscribe reaches the same recovery the refreshes do
• Any other failure is surfaced rather than swallowed
• Tests cover both paths; npm run local:gate green