fix(ci): restore Prismatix lint checks

[gthgomez]

Summary

• adds root ESLint config so npm run lint has a project config
• removes unused symbols and fixes regex lint issues without changing router behavior
• updates debate payload test expectation for contrarian instructions

Verification

• npm ci
• npm run type-check
• npm run lint
• npm run test
• npm run build
• deno check ./supabase/functions/router/index.ts
• deno lint ./supabase/functions/router/