port(go): omit bare OpenAI catalog rows without openai provider (#643)

[Wibias]

Source

• dev merge: fix(catalog): omit bare OpenAI models without openai provider #643 (f19a73c3, closes Bare OpenAI models are advertised but return 404 when canonical openai provider is not configured #636)
• dev2-go carry: fix(catalog): carry bare-OpenAI catalog omit onto dig2-go (#643) #681

Gap

TS catalog sync skips bare gpt-* / native OpenAI rows when providers exist but no enabled canonical openai forward provider is configured, and NoEnabledOpenAiProviderError points at ocx provider add openai && ocx sync && ocx restart.

Go has go/internal/codex/catalog_sync.go / visibility / roster — needs the same omit + error wording parity.

Done when

Go catalog sync matches the TS oracle with tests green on dev2-go.

[github-actions]

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