refactor(banks): add Bank::availableForUser scope (#480)

## 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).

app/Http/Controllers/BudgetController.php

@@ -95,10 +95,7 @@ class BudgetController extends Controller
             ->get(['id', 'name', 'name_iv', 'encrypted', 'bank_id', 'type', 'currency_code']);
 
         $banks = Bank::query()
-            ->where(function ($q) use ($user) {
-                $q->whereNull('user_id')
-                    ->orWhere('user_id', $user->id);
-            })
+            ->availableForUser($user)
             ->orderBy('name')
             ->get(['id', 'name', 'logo']);
 

app/Http/Controllers/CashflowController.php

@@ -27,10 +27,7 @@ class CashflowController extends Controller
             ->get(['id', 'name', 'name_iv', 'encrypted', 'bank_id', 'type', 'currency_code']);
 
         $banks = Bank::query()
-            ->where(function ($q) use ($user) {
-                $q->whereNull('user_id')
-                    ->orWhere('user_id', $user->id);
-            })
+            ->availableForUser($user)
             ->orderBy('name')
             ->get(['id', 'name', 'logo']);
 

app/Http/Controllers/OnboardingController.php

@@ -19,8 +19,7 @@ class OnboardingController extends Controller
         $user = $request->user();
 
         $banks = Bank::query()
-            ->whereNull('user_id')
-            ->orWhere('user_id', $user->id)
+            ->availableForUser($user)
             ->orderBy('name')
             ->get(['id', 'name', 'logo']);
 

app/Http/Controllers/Settings/BankController.php

@@ -14,11 +14,7 @@ class BankController extends Controller
 {
     public function index(Request $request): JsonResponse
     {
-        $query = Bank::query()
-            ->where(function (Builder $q) {
-                $q->whereNull('user_id')
-                    ->orWhere('user_id', auth()->id());
-            });
+        $query = Bank::query()->availableForUser($request->user());
 
         $search = trim((string) $request->input('search', ''));
 

app/Http/Controllers/TransactionController.php

@@ -82,10 +82,7 @@ class TransactionController extends Controller
             ->get(['id', 'name', 'name_iv', 'encrypted', 'bank_id', 'type', 'currency_code']);
 
         $banks = Bank::query()
-            ->where(function ($q) use ($user) {
-                $q->whereNull('user_id')
-                    ->orWhere('user_id', $user->id);
-            })
+            ->availableForUser($user)
             ->orderBy('name')
             ->get(['id', 'name', 'logo']);
 
@@ -127,10 +124,7 @@ class TransactionController extends Controller
             ->get(['id', 'name', 'name_iv', 'encrypted', 'bank_id', 'type', 'currency_code']);
 
         $banks = Bank::query()
-            ->where(function ($q) use ($user) {
-                $q->whereNull('user_id')
-                    ->orWhere('user_id', $user->id);
-            })
+            ->availableForUser($user)
             ->orderBy('name')
             ->get(['id', 'name', 'logo']);
 

app/Models/Bank.php

@@ -3,6 +3,7 @@
 namespace App\Models;
 
 use Database\Factories\BankFactory;
+use Illuminate\Database\Eloquent\Builder;
 use Illuminate\Database\Eloquent\Concerns\HasUuids;
 use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
@@ -21,6 +22,20 @@ class Bank extends Model
         'user_id',
     ];
 
+    /**
+     * Scope to banks visible to the given user: public banks plus their own.
+     *
+     * @param  Builder<Bank>  $query
+     * @return Builder<Bank>
+     */
+    public function scopeAvailableForUser(Builder $query, User $user): Builder
+    {
+        return $query->where(function (Builder $q) use ($user) {
+            $q->whereNull('user_id')
+                ->orWhere('user_id', $user->id);
+        });
+    }
+
     /** @return BelongsTo<User, $this> */
     public function user(): BelongsTo
     {