fix: retry OpenAI model sync after TLS EOF

[GitClound]

Summary

• Retry OpenAI API-key model-list sync with a Chrome TLS fingerprint when the standard upstream request ends in TLS EOF.
• Retry the Chrome request once for transient EOF or connection-reset errors.
• Keep the fallback scoped to OpenAI API-key accounts; other platforms and account types keep their current behavior.

Validation

• go test ./internal/service
• go vet ./internal/service
• Live integration test with the affected account and an injected EOF completed successfully.

The live test is behind the integration build tag and requires SUB2API_LIVE_OPENAI_BASE_URL and SUB2API_LIVE_OPENAI_API_KEY; credentials are not included in this change.

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