fix: check both 'expected' and 'output' field names in test cases

security: harden API + optimize performance

feat: switch from Piston to onlinecompiler.io API

feat: add /stress-test endpoint for load testing (bypasses Supabase)

refactor: migrate to public Piston API with Redis rate limiter

Update main.py to use API Key verification instead of JWT

Replace Piston with custom subprocess executor

Add runtime, FastAPI main, and worker