## Why
### Problem
The default income categories lacked coverage for self-employed
individuals (freelancers, contractors, sole traders). Users in this
segment had no accurate category to classify their primary income
source.
## What
### Changes
- Added `Self-Employment Income` income category (icon: `Briefcase`,
color: `green`) to `CreateDefaultCategories::getBaseCategories()`
- Added Spanish translation `Ingresos por trabajo autónomo` to
`getSpanishTranslations()`
- Updated category count assertions in `CategoryTest` from 63 → 64
## Verification
### Tests
- `php artisan test --compact --filter="default categories"` — 2 tests,
7 assertions, all passing
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