feat: enable environment-based logging control via ENVIRONMENT and LOG_LEVEL

[MetehanAydemir]

Summary

Resolves #486. The ENVIRONMENT and LOG_LEVEL values in backend/app/core/constants.py were hardcoded ("development" / "DEBUG"), so the corresponding environment variables — already plumbed into the containers by docker-compose.yml — had no effect. Logging behavior could not be changed per environment without editing code.

This reads both values from the environment, with the previous hardcoded values kept as defaults:

ENVIRONMENT = os.getenv("ENVIRONMENT", "development").lower()
LOG_LEVEL = os.getenv("LOG_LEVEL", "DEBUG").upper()

ENVIRONMENT's effect is logging-only (console format JSON vs. colored, level); it does not gate security, DB, or CORS behavior.

Testing

Verified against the built backend image via docker compose:

• Default env → development / DEBUG (unchanged; no regression)
• ENVIRONMENT=production LOG_LEVEL=WARNING → code now resolves production / WARNING
• Under ENVIRONMENT=production, logs are emitted as JSON (was colored human-readable before)
• Live container healthy after rebuild: GET /health and GET /api/v1/nodes both return 200