fix(balances): allow zero on CSV import reference + lock contract with tests

Extend the zero-balance fix to the CSV-import reference balance field (same
root cause; the compute path already gates on referenceBalance !== null, so an
explicit 0 is a valid anchor). Drop the now-orphaned 'Please enter a balance'
translation and add feature tests asserting a zero balance can be stored and
set as the current balance.

lang/es.json

@@ -1240,7 +1240,6 @@
     "Pink": "Rosa",
     "Platform": "Plataforma",
     "Please describe the problem and what you were doing when it happened. Keep the details below — they help us debug.": "Describe el problema y qué estabas haciendo cuando ocurrió. Conserva los detalles de abajo: nos ayudan a depurar.",
-    "Please enter a balance": "Por favor, ingresa un balance",
     "Please enter a bank name.": "Por favor, ingresa un nombre de banco.",
     "Please enter an account name.": "Por favor, ingresa un nombre de cuenta.",
     "Please enter your new password below": "Por favor ingresa tu nueva contraseña a continuación",

lang/fr.json

@@ -1199,7 +1199,6 @@
     "Pink": "Rose",
     "Platform": "Plate-forme",
     "Please describe the problem and what you were doing when it happened. Keep the details below — they help us debug.": "Décrivez le problème et ce que vous faisiez lorsqu'il s'est produit. Conservez les détails ci-dessous : ils nous aident à déboguer.",
-    "Please enter a balance": "Veuillez saisir un solde",
     "Please enter a bank name.": "Veuillez saisir un nom de banque.",
     "Please enter an account name.": "Veuillez saisir un nom de compte.",
     "Please enter your new password below": "Veuillez entrer votre nouveau mot de passe ci-dessous",

resources/js/components/transactions/import-step-mapping.tsx

@@ -428,7 +428,6 @@ export function ImportStepMapping({
                                         value={referenceBalance ?? 0}
                                         onChange={onReferenceBalanceChange}
                                         currencyCode={currencyCode}
-                                        required
                                     />
                                     {referenceBalancePrefilled && (
                                         <p className="text-xs text-muted-foreground">

tests/Feature/AccountBalanceControllerTest.php

@@ -280,6 +280,47 @@ it('can store balance without invested_amount', function () {
     ]);
 });
 
+it('can store a zero balance', function () {
+    $user = User::factory()->create();
+    $account = Account::factory()->for($user)->create();
+
+    $response = $this->actingAs($user)->postJson("/api/accounts/{$account->id}/balances", [
+        'balance' => 0,
+        'balance_date' => now()->subDays(5)->toDateString(),
+    ]);
+
+    $response->assertStatus(201)
+        ->assertJsonPath('data.balance', 0);
+
+    $this->assertDatabaseHas('account_balances', [
+        'account_id' => $account->id,
+        'balance' => 0,
+    ]);
+});
+
+it('can update the current balance to zero', function () {
+    $user = User::factory()->create();
+    $account = Account::factory()->for($user)->create();
+
+    AccountBalance::factory()->for($account)->create([
+        'balance_date' => now()->toDateString(),
+        'balance' => 100000,
+    ]);
+
+    $response = $this->actingAs($user)->putJson("/api/accounts/{$account->id}/balance/current", [
+        'balance' => 0,
+    ]);
+
+    $response->assertSuccessful()
+        ->assertJsonPath('data.balance', 0);
+
+    $this->assertDatabaseHas('account_balances', [
+        'account_id' => $account->id,
+        'balance_date' => now()->toDateString(),
+        'balance' => 0,
+    ]);
+});
+
 it('validates store balance must be an integer', function () {
     $user = User::factory()->create();
     $account = Account::factory()->for($user)->create();