fix: project Responses token preflight request

[pcvantol]

Summary

• Project the canonical Responses generation request into the documented Responses input-token count request shape.
• Retain all token-relevant fields, including the strict structured-output schema.
• Exclude only endpoint-unsupported store and max_output_tokens; canonical context validation continues to bind the output limit.
• Fail closed before Keychain resolution or transport if the generation shape changes.

Validation

• Focused OpenAI adapter security tests pass.
• Full repository validation passes: 363 tests and offline projection validation.

No provider generation, Action derivation, or Action execution was run.