feat: Add nektos/act config for local CI workflow testing

[mark-e-deyoung]

Description

Add configuration for nektos/act to enable running GitHub Actions workflows locally.

Why

Provides faster feedback loop for workflow changes without pushing to GitHub.

Status

Deferred — local test runners already provide fast feedback for code changes. Revisit when:

• CI debugging becomes a recurring time sink
• Workflow complexity increases significantly
• A contributor without CI access needs to test workflow changes

References

• act: https://github.com/nektos/act
• Item G from testing audit (2026-07-05)