impr(language): improve Oromo word lists (@NaolMengistu) (#7730)

## What this changes
Improves all three Afaan Oromo word list files used in the typing test.

## Files changed
- oromo.json
- oromo_1k.json
- oromo_5k.json

## Changes made
- Clean up misspelled entries
- Remove English and other non-Oromo words
- Replace them with common Oromo vocabulary
- Sort all three lists by frequency

## Word count verification
- oromo.json: 645 words ✓
- oromo_1k.json: 1000 words ✓
- oromo_5k.json: 5000 words ✓

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Co-authored-by: Jack <jack@monkeytype.com>

Author: NaolMengistu