fix(sse): export PROVIDER_BREAKER_FAILURE_STATUSES so chat.ts stops throwing ReferenceError

Base-red slice 4 (single root cause across the whole handleChat cluster).

src/sse/handlers/chat.ts:1273 references PROVIDER_BREAKER_FAILURE_STATUSES to decide
whether an all-rate-limited provider result should trip the provider breaker, but the
constant was only a FILE-LOCAL const in chatPredicates.ts (a refactor extracted it out
of chat.ts and never re-exported it). Every request that reached that branch threw
`ReferenceError: PROVIDER_BREAKER_FAILURE_STATUSES is not defined`, so the global
fallback and breaker-gate paths blew up — surfacing as "All models failed |
PROVIDER_BREAKER_FAILURE_STATUSES is not defined" and breaking the handleChat coverage
tests (combo-error passthrough, 503 for cooled-down/open-breaker, budget-error, model
cooldown, body-derived retry-after, non-JSON rate-limit bodies).

Fix: export the const from chatPredicates.ts and import it in chat.ts (one canonical
definition, restoring the pre-refactor behavior).

Validated: chat-route-coverage 15/0 (was 12/3), chat-cooldown-aware-retry 6/0,
chat-rate-limit-body-lock 2/0; breaker guards (7907, combo-breaker-429, openrouter-6842)
unchanged; typecheck:core clean.

src/sse/handlers/chat.ts

@@ -77,6 +77,7 @@ import {
   isAntigravityMissingProjectError,
   PROVIDER_BREAKER_FAILURE_STATUSES,
   shouldTripProviderBreakerForResult,
+  PROVIDER_BREAKER_FAILURE_STATUSES,
 } from "./chatPredicates";
 import { connectionHasExtraKeys } from "@omniroute/open-sse/services/apiKeyRotator.ts";
 import {