fix(cli): restore list category fallback for unknown providers

[developersdigest]

firecrawl list shopping probes shopping as a provider before trying it as a category. The API now rejects unknown providers, so that error previously stopped the category fallback.

Allow the existing fallback for the unknown-provider code or the API's specific unknown/unavailable-provider message. Preserve provider-first precedence and continue surfacing rate-limit, authentication, transport and other errors. No API or version changes.

Validation: TypeScript build, formatting, and compiled CLI regression against a local API fixture. The regression checks the reported shopping failure and that rate-limit errors do not trigger fallback.

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Summary by cubic

Restores the category fallback in firecrawl list so commands like firecrawl list shopping still work when the API rejects unknown providers.

Previously, the API's unknown-provider error stopped the existing category fallback, so browsing a category by name failed. Now the fallback proceeds when the API reports an unknown or unavailable provider, while rate-limit, authentication, transport, and other errors still surface as failures. Provider-first precedence is unchanged, and there are no API or version changes.

^{Written for commit cdcfc2c. Summary will update on new commits.}