Scope O2 linter push runs to pushed commit range

[Copilot]

The O2 linter workflow was failing on push because it linted the full branch divergence from master, surfacing unrelated pre-existing violations. This change narrows push-time linting to files introduced by the pushed commit range while keeping PR behavior unchanged.

• Workflow diff scope

  • On push, file selection now uses ${{ github.event.before }}..${{ github.sha }} instead of origin/${{ env.BRANCH_BASE }}....
  • On first push to a new branch (before is all-zero SHA), file selection falls back to files in ${{ github.sha }}.

• Event-specific behavior preserved

  • pull_request_target path is unchanged and still diffs against the base branch via merge-base semantics.

• Updated run logic (excerpt)

if [[ "${{ github.event_name }}" == "push" ]]; then
  if [[ "${{ github.event.before }}" == "0000000000000000000000000000000000000000" ]]; then
    readarray -t files < <(git show --diff-filter d --name-only --pretty=format: ${{ github.sha }})
  else
    readarray -t files < <(git diff --diff-filter d --name-only ${{ github.event.before }} ${{ github.sha }})
  fi
else
  readarray -t files < <(git diff --diff-filter d --name-only origin/${{ env.BRANCH_BASE }}...)
fi