eslint@9, prettier

[scottanderson]

Features

• Migrate to eslint@9.
  • Migrate various config files to the modern ESM *.config.mjs format, so eslint can detect and handle them correctly.
• Report eslint errors and warnings as github annotations using eslint-gha-formatter.
  • This CI check is currently disabled. See the steps below to enable it.
  • Annotations will appear in the files view after the github action runs.
• Add common stylistic and typescript-eslint rules.
  • The chosen settings reflect the existing code style, measured as number of lines affected.
• Reduce rules with violations to warn.
  • These warnings can be addressed in separate PRs.

Dependencies

This change includes code from:

• Update build.yml to allow pushes to any branch #172

Next steps

After merging this PR, complete the following steps to enable CI enforcement of lint and style rules:

Step 1: Auto-fix all remaining lint and style check failures:

• npm run lint:fix #173
  This PR was generated by running:

npm run lint:fix

Step 2: Enable pre-commit hook and CI enforcement:

• Pre-commit hooks and CI enforcement for eslint and prettier  #174

npm i -D lint-staged

     "lint": "eslint && prettier -c .",
-    "lint:ci": "true # TODO: eslint -f gha && prettier -c .",
+    "lint:ci": "eslint -f gha && prettier -c .",
     "lint:fix": "eslint --fix && prettier -w .",

[scottanderson]

The auto-formatter incorrectly removes the closing </p> tag due to a bug, causing a secondary build failure because the unclosed tag is invalid JSX. The correct formatting is included here so that the code can be formatted by running npm run lint:fix without creating this build failure.