## What
The "public banks + user's own banks" query was repeated in **5
controllers** (Transaction ×2, Settings/Bank, Budget, Cashflow,
Onboarding).
New `Bank::availableForUser($user)` scope; all 5 sites use it.
Bonus: the Onboarding variant had no `where()` grouping around
`whereNull/orWhere` — harmless today (no other constraints) but a latent
precedence bug. The scope always groups.
## Stats
- **-31 / +24 lines**, 5 call sites → 1 definition
## Checks
- `php artisan test
--filter="Bank|Transaction|Budget|Cashflow|Onboarding"` — 612 passed
(2707 assertions), 1 skipped
- `vendor/bin/pint --dirty` — pass
Part of duplication-removal series (#475–#479).
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