fix(providers): list gemini-business models in the registry (#12389)

GET /v1/providers/gemini-business/models returned nothing because gemini-business had no RegistryEntry: the listing route resolves the provider through getRegistryEntry and filters the unified catalog by owned_by, and open-sse/config/providers/index.ts only registered gemini and gemini-web.

Adds a registry entry mirroring gemini_webProvider — id gemini-business, alias gembiz, cookie auth — with the twelve ids from the executor's MODEL_CATEGORY_MAP. Each model is declared toolCalling: false, supportsReasoning: false, the same live-behaviour contract applied to gemini-web in #9356: the executor returns plain text, hard-wires the thinking mode and parses no tool calls.

Reconciled on merge: the only conflict was the reserved-prefix count assertion, which the tip had moved. Took the tip's text and measured the real value with this PR applied — 406 to 408, the gemini-business id plus its gembiz alias — rather than carrying the branch's number.

Validated in a combined worktree with all 25 PRs of this batch boarded together (typecheck:core clean, 443/443 node-runner plus 14/14 vitest, all static gates green), and re-verified standalone on the current tip after the other 24 landed: 33/33 across provider-node-reserved-prefix, gemini-business-model-registry-12107 and web-cookie-validation-fallback, with check:provider-consistency OK at 272 REGISTRY entries and 355 canonical providers.

Thanks @pacocartones.