[1sakshm]

Description

GET /zipcode/lookup-address reported client mistakes and Nominatim outages as FireForm server errors. This fixes the status and error codes in the route; the geocoding service itself is unchanged.

Request / situation	Before	After
address= (empty)	200 []	422 VALIDATION_ERROR, field query.address
address=%20%20%20 (only spaces)	sent to Nominatim, then 500 INTERNAL_ERROR	422 VALIDATION_ERROR, Nominatim not called
Nominatim error (GeocoderServiceError)	500 INTERNAL_ERROR	502 GEOCODING_FAILED
Nominatim timeout	504 with error_code: "ERROR"	504 GEOCODING_TIMEOUT
Valid address / no results	200	200 (unchanged)

• Blank addresses raise RequestValidationError, the same way weather.py and input.py reject bad input.
• The service already turns GeocoderServiceError into RuntimeError and GeocoderTimedOut into TimeoutError; the route now maps those to 502 / 504 with specific error codes. Any other exception is still a 500.

No frontend change needed: the address lookup modal already shows the backend's message.

Fixes #740

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Added TestZipcodeEndpoints in tests/test_api.py (there were no zipcode tests before), with Nominatim mocked:
  • blank address ("" and " ") → 422 and Nominatim is never called
  • GeocoderServiceError → 502 GEOCODING_FAILED
  • GeocoderTimedOut → 504 GEOCODING_TIMEOUT
  • no results → 200 []
  • On development the first four fail and the last passes
• Checked the "Before" column for the whitespace case against the real Nominatim API
• Full suite: python -m pytest tests/ → 318 passed
• ruff check app/ → all checks passed

Test Configuration:

• Python version: 3.11
• Docker/Compose version: N/A (tests run locally)
• OS: Windows 11

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• The Lint workflow check passes on this PR ✅
• The Tests workflow check passes on this PR ✅