Local-agent login imports (Codex API et al.) declare the provider protocol
at the top level of the payload (protocol: "openai_responses") and carry no
capabilities array. parseProviders dropped that field, so the saved provider
ended up with neither protocol nor capabilities and the gateway fell back to
the default openai_chat_completions adapter. For Responses-only backends
(chatgpt.com/backend-api/codex) every request then 404s against a
non-existent /chat/completions route.
Synthesize a single capability from the top-level protocol (and the
provider's base URL) when no explicit capabilities are configured, reusing
the existing protocol normalization used for capability items. Explicit
capabilities still win. Fixes#1619.
ezra-quemuel