Add Axe accessibility checks for pull requests

[nonprofittechy]

Summary

• add a self-contained Playwright/Axe accessibility check for pull requests to main
• cover public, signed-in, and primary filing screens using deterministic local fixture data
• audit the claim-party dialog separately and upload JSON results on every run
• fix accessible labels and color contrast findings exposed by the new checks

Validation

• pre-commit hooks: ruff, djlint, CSS/JS formatting, ESLint, ty, Bandit, and migration check
• focused Playwright/Axe runs for primary filing screens and the claim-party dialog