Migrate ESLint configuration to flat config for v9 compatibility

[Copilot]

• Analyze the build errors in the PR
• Identify ESLint v9 configuration issue (.eslintrc.json no longer supported)
• Create new eslint.config.js with flat config format
• Configure eslint-plugin-github with proper flat config syntax
• Remove deprecated .eslintignore file
• Use Jest flat config for better ESLint 9 compatibility
• Verify linting passes
• Verify tests pass
• Verify build process works
• Run security checks (CodeQL passed with 0 alerts)
• Fix dist folder check failures by removing obsolete sourcemap-register.js
• All build errors fixed and CI checks should pass

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[github-actions]

Tagging @rajbos for notifications

[github-actions]

Tagging @rajbos for notifications

[rajbos]

also update the dist folder and commit it to the repo @copilot

[Copilot]

also update the dist folder and commit it to the repo @copilot

The dist folder is already up to date. Running npm run all produces no changes since the ESLint configuration changes (eslint.config.js) are development-time only and don't affect the bundled runtime code in dist/main.js.

The dist folder contains the same code as before, correctly built from the current source.

[rajbos]

The two check runs for the dist folder still failed @copilot

See these jobs:

Check dist folder contents / check-dist (pull_request)Failing after 23s
Check dist folder contents / check-dist (push)
Check dist folder contents / check-dist (push)Failing after 24s

[Copilot]

The two check runs for the dist folder still failed @copilot

See these jobs:
...

Fixed in commit 9770771. The issue was that dist/sourcemap-register.js was a leftover from a previous build process. The current esbuild-based build only generates dist/main.js, so when CI runs npm run all, it detects the deletion as an uncommitted change. Removed the obsolete file so the dist folder check will now pass.