fix: resolve oai Summary struct breaking change in OpenAI responses request

[ashprakasan]

Problem

After the dependency upgrade in #2474 , the CI was failing
because the Summary struct was removed/renamed in the new version of the
oai crate.

Changes

• Updated oai::Summary usage in crates/forge_repo/src/provider/openai_responses/request.rs
  to use the new API shape (lines 71 and 911)

Testing

• Reproduced the issue locally and verified the fix compiles successfully
• CI should pass with these changes

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