chore: remove Copilot setup workflow

[ShoGinn]

Summary

• remove the Copilot-specific dependency bootstrap workflow
• keep AGENTS.md and the repository-wide Copilot instructions as the onboarding sources of truth
• avoid installing both dependency trees before every cloud-agent task

Rationale

The repository already has standard locked dependency manifests and documented bootstrap commands. The special setup workflow duplicated that configuration, added maintenance overhead, and performed unnecessary setup for documentation-only tasks.

Validation

• pre-commit run --all-files
• commit-time ty check
• pre-push fast backend tests
• pre-push frontend typecheck
• pre-push frontend tests

This PR deletes only .github/workflows/copilot-setup-steps.yml.

[railway-app]

🚅 Deployed to the tax-tracker-pr-87 environment in endearing-eagerness

Service	Status	Web	Updated (UTC)
tax-tracker	✅ Success (View Logs)	Web	Aug 2, 2026 at 12:20 am

[Copilot]

Pull request overview

Removes the repository’s Copilot cloud-agent bootstrap workflow so onboarding and dependency setup are driven by the existing documented commands (e.g., in AGENTS.md) rather than a dedicated Copilot setup workflow.

Changes:

• Deleted .github/workflows/copilot-setup-steps.yml, removing the pre-agent GitHub Actions job that installed Node/pnpm and Python/uv dependencies.
• Eliminated the workflow’s self-triggering behavior on edits to that file.