chore: migrate ESLint to flat config and add SARIF scanning

[wrigjl]

Summary

• Replaces .eslintrc.json with eslint.config.js (ESLint 9 flat config format), required for ESLint 10 compatibility when upstream parser support lands
• Updates lint script from next lint (removed in Next.js 16) to eslint .
• Renames codeql.yml → code-analysis.yml and adds an eslint job that uploads results to the GitHub Security tab via SARIF
• Adds eslint-results.sarif to .gitignore

Notes

ESLint 10 was investigated but blocked by @babel/eslint-parser (bundled in Next.js) and @typescript-eslint not yet implementing addGlobals required by ESLint 10. Tracked upstream at babel/babel#17791 and typescript-eslint/typescript-eslint#11829. This flat config migration means bumping to ESLint 10 will be a one-line change once those are resolved.

Test plan

• npm run lint runs ESLint and reports findings
• npx eslint . --format @microsoft/eslint-formatter-sarif --output-file eslint-results.sarif produces a valid SARIF file
• CI workflow runs both CodeQL and ESLint jobs

🤖 Generated with Claude Code

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