[Good First Issue] Add bbox coordinate validation to PredictRequest

[Oshgig]

Overview

The PredictRequest schema accepts a bbox field but does not validate that the coordinates are geographically valid. A malformed bbox (e.g., lat > 90, lon > 180, or min > max) causes a silent failure or confusing error during GEE querying.

Scope

• Add Pydantic validators to PredictRequest.bbox in src/climatevision/api/schemas.py (or main.py if schemas are inline)
• Validate:
  • Exactly 4 elements: [west, south, east, north]
  • -180 <= longitude <= 180
  • -90 <= latitude <= 90
  • west < east and south < north
• Return a clear 422 Unprocessable Entity with descriptive error message
• Add pytest test in tests/test_api.py covering at least 3 invalid cases and 1 valid case

Acceptance Criteria

• POST /api/predict with bbox: [200, 10, 30, 40] returns 422 with "Invalid longitude: 200"
• POST /api/predict with bbox: [-60, -15, -45, -5] succeeds as before
• All new tests pass in CI

Resources

• src/climatevision/api/main.py — PredictRequest schema
• tests/test_api.py — existing API tests
• Pydantic field_validator docs

Difficulty: Beginner-friendly
Labels: good first issue, backend, api, validation