refactor: align scoring evidence and API efficiency

[SamoTech]

Scope

• Count commits through GitHub search instead of materializing all commits.
• Detect documentation files without relying on a potentially truncated recursive tree.
• Redefine PR Velocity as merged-PR throughput over the same 90-day window as Commit Activity.
• Bump the Action report version to 2.1.0.

Verification

Deterministic regression checks plus the real Action/release preflight will verify the change before publication.

[chatgpt-codex-connector]

You have reached your Codex usage limits for code reviews. You can see your limits in the Codex usage dashboard.
To continue using code reviews, you can upgrade your account or add credits to your account and enable them for code reviews in your settings.