[Frontend] Add localized pluralization and unit formatting tests

## Problem
Medication quantities, appointment durations, and pet counts can be grammatically or numerically incorrect across locales.
## Acceptance criteria
- All user-facing counts and units use centralized locale-aware formatters.
- Zero, one, few, and many forms are covered where supported.
- Medical units are never converted implicitly without displaying the unit.
- Tests cover English, Spanish, RTL fixtures, decimals, and missing translations.

No files or test entry points are named. Start by locating the centralized locale-aware formatters and existing localization tests, then run the relevant frontend test suite; done means coverage for English, Spanish, RTL fixtures, decimals, missing translations, plural forms, and explicit medical units.

Written by the indexing model from the issue text.