feat(devops): emit structured JSON logs (#38)

[MariaEduardaBatt]

Implementacao de logs JSON estruturados no backend conforme issue #38.

Criterios:

• Backend emite linhas JSON estruturadas
• Logs carregam request_id, user_id e duration_ms

Arquivos:

• logging_config.py (novo) - JsonFormatter + RequestIdFilter
• app.py - hooks before/after_request
• routes/run_ws.py - logs com user_id, duration_ms
• routes/compile.py - logs com user_id, duration_ms

Testes: 66 passed, 1 failed (pre-existente)