Track who paid each depense, with a "Commun" (shared) fallback

Adds a "payé par" field to transactions and recurring transactions:
either a household member or null (shared/common expense). No per-
member account balances — this is purely a "who paid" label, the
household's overall balance is unchanged and unaffected by any
filtering.

- paid_by_user_id nullable FK on transactions and recurring_transactions
- Suivi: "payé par" selector on both entry forms (desktop dropdown,
  mobile buttons), a filter above the transaction table, a "payé par"
  column, and a summary tile showing this month's depenses grouped
  by payer (including Commun)
- Recurring transactions carry paid_by_user_id onto the transaction
  they generate when confirmed
- Running balance is computed from all transactions regardless of
  the payer filter, so it never gets skewed by the active filter

11 new Pest tests (assignment, common fallback, non-member rejection,
filter isolation from the balance calc, per-payer summary, recurring
propagation). 69/69 total pass, Pint clean, verified end-to-end on
production data (desktop + mobile, test row created and removed).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/Feature/RecurringTransactionTest.php

@@ -65,3 +65,48 @@ it('deletes a recurring transaction', function (): void {
 
     expect(RecurringTransaction::find($recurring->id))->toBeNull();
 });
+
+it('assigns a recurring transaction to a household member', function (): void {
+    $owner = User::factory()->create();
+    $member = User::factory()->create();
+    $household = $owner->currentHousehold;
+    $member->households()->attach($household->id, ['role' => 'member']);
+
+    $category = $household->categories()->create(['name' => 'Loyer', 'type' => 'depense', 'position' => 1]);
+
+    Livewire::actingAs($owner)
+        ->test(Index::class)
+        ->set('name', 'Loyer')
+        ->set('categoryId', $category->id)
+        ->set('amount', '1200')
+        ->set('dayOfMonth', '5')
+        ->set('paidByUserId', (string) $member->id)
+        ->call('add');
+
+    $recurring = $household->recurringTransactions()->first();
+
+    expect($recurring->paid_by_user_id)->toBe($member->id);
+});
+
+it('carries the recurring paid-by user onto the generated transaction', function (): void {
+    $this->travelTo(now()->setDate(2026, 3, 10));
+
+    $owner = User::factory()->create();
+    $member = User::factory()->create();
+    $household = $owner->currentHousehold;
+    $member->households()->attach($household->id, ['role' => 'member']);
+
+    $category = $household->categories()->create(['name' => 'Loyer', 'type' => 'depense', 'position' => 1]);
+    $recurring = $household->recurringTransactions()->create([
+        'category_id' => $category->id, 'paid_by_user_id' => $member->id,
+        'name' => 'Loyer', 'amount' => 1200, 'day_of_month' => 5,
+    ]);
+
+    Livewire::actingAs($owner)
+        ->test(App\Livewire\Suivi\Index::class)
+        ->call('confirmRecurrence', $recurring->id, '1200');
+
+    $transaction = $household->transactions()->where('recurring_transaction_id', $recurring->id)->first();
+
+    expect($transaction->paid_by_user_id)->toBe($member->id);
+});