chore: onboard repository agents

[ShoGinn]

Summary

• replace stale Claude-specific guidance with canonical cross-agent instructions
• add concise Copilot repository instructions for cloud agent and code review
• add a pinned Copilot setup workflow for Python and frontend dependencies

Validation

• pre-commit run --all-files
• Ruff format and lint checks
• ty type checking
• 376 backend tests (89.31% overall coverage)
• service coverage gate (92.72%)
• 34 frontend tests, typecheck, lint, and production build
• 2 Playwright end-to-end tests
• FastAPI health smoke test

Docker smoke testing was not run because the local Docker daemon was unavailable. Security scanning and the network-backed PSLmodels refresh were not run because this documentation and workflow change does not affect them.

[railway-app]

🚅 Deployed to the tax-tracker-pr-85 environment in endearing-eagerness

Service	Status	Web	Updated (UTC)
tax-tracker	✅ Success (View Logs)	Web	Aug 1, 2026 at 11:30 pm

[Copilot]

Pull request overview

This PR onboards cross-agent repository guidance by removing Claude-specific documentation and introducing canonical instructions for automated agents and GitHub Copilot, plus a workflow to bootstrap the Copilot cloud agent environment consistently for both backend (Python/uv) and frontend (Node/pnpm).

Changes:

• Remove the legacy CLAUDE.md guide in favor of a unified agent guide.
• Add AGENTS.md as the primary repository agent guide (product boundaries, architecture map, and validation commands).
• Add GitHub Copilot-specific instructions and a pinned copilot-setup-steps workflow to install locked backend/frontend dependencies.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
CLAUDE.md	Removes stale Claude-specific and outdated guidance.
AGENTS.md	Adds the canonical cross-agent repository guide (scope, architecture, workflows, validation).
.github/workflows/copilot-setup-steps.yml	Adds a workflow to set up Python/uv and Node/pnpm dependencies for Copilot cloud agents.
.github/copilot-instructions.md	Adds concise Copilot repository instructions aligned with AGENTS.md.

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