refactor(policies): extract HandlesUserOwnership trait (#478)
## What
`CategoryPolicy`, `LabelPolicy`, `TransactionPolicy`,
`AutomationRulePolicy` were structurally identical: `update`/`delete`
check `$user->id === $model->user_id`, everything else returns `false`.
`AccountPolicy` same + ownership `view`.
New `app/Policies/Concerns/HandlesUserOwnership` trait; the 5 policies
now use it (Account keeps its `view` override).
`BudgetPolicy` and `RealEstateDetailPolicy` untouched — different
semantics (all-allowed / ownership via parent account).
## Stats
- **-252 / +112 lines**
## Checks
- `php artisan test
--filter="Categor|Label|Transaction|AutomationRule|Account|Polic"` — 607
passed (2887 assertions), 1 skipped
- `vendor/bin/pint --dirty` — pass
Part of duplication-removal series (#475, #476, #477).
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