fix(tui): defer buffered gateway events to stop dashboard chat #301 (#36658)

[kshitijk4poor]

Summary

Dashboard /chat works again after hermes update — it was throwing Minified React error #301 ("Too many re-renders") and rendering nothing.

Root cause: Dashboard /chat spawns the TUI attached to the dashboard's in-memory gateway (HERMES_TUI_GATEWAY_URL). In attach mode the gateway is already running, so it replays gateway.ready / session.info the instant the socket connects — those land in GatewayClient.bufferedEvents before the consumer's mount-time subscribe effect (useMainApp.ts) calls drain(). drain() emitted the buffered events synchronously, so the gateway.ready handler's patchUiState / setHistoryItems cascade ran while React was still inside its first commit → #301. Spawn / inline / sidecar modes never hit it: their gateway.ready arrives only after the Python child boots, on a later async tick.

Changes

• ui-tui/src/gatewayClient.ts — drain() defers the buffered-event replay to the next microtask and keeps subscribed false until that microtask runs, so a LIVE event arriving in the gap keeps buffering (publish() pushes when !subscribed) instead of jumping ahead of the chronologically-earlier replayed events; the flush re-drains right after flipping subscribed, preserving FIFO. A drainGeneration token (bumped in resetStartupState) makes a queued flush a no-op if the transport was reset/killed meanwhile.
• ui-tui/src/__tests__/gatewayClient.test.ts — 2 regression tests: (1) drain() does not dispatch buffered events synchronously; (2) a live event arriving in the post-drain / pre-microtask window still delivers BEHIND the earlier-buffered event (FIFO).

Same class of fix as #44528 (deferred a config RPC for an embedded-dashboard #301) — the defect is event-delivery timing at the transport seam, not hook-dep identity in the component.

Validation

	Synchronous drain() (before)	Deferred drain() (after)
attach-mode gateway.ready replay	fires inside first commit → #301	fires on microtask, after commit ✓
live event in post-drain gap	could reorder ahead of buffered	stays FIFO behind buffered ✓

• npx vitest run src/__tests__/gatewayClient.test.ts → 13 passed. Proven RED→GREEN: reverting drain() to the synchronous loop fails the 2 new tests, restoring passes.
• npx tsc --noEmit -p tsconfig.json → clean. npx eslint on changed files → clean.

Closes #36658