Addresses the @claude review of #1611: the event registry is now keyed by
(client, fn) rather than event name alone, and a new `fireClientEventFor(client,
…)` helper fires a single client's listeners. The "ignores auth lifecycle events
from a non-selected server" test now fires ambient/recovered/oauthError for ONLY
the non-selected client and asserts no message appears — so removing the
`selectedServerRef.current !== serverName` guard would fail the test — then fires
for the selected client to confirm it does act. Coverage of App.tsx is unchanged
(92.23 / 90.20 / 92.85 / 92.68); existing fire-all `fireClientEvent` behavior is
preserved.
Part of #1610.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S3fTN8H3R8YV4yUGvZjYnX
1f7ef9184c