feat: ETA côtier — transformer la map en outil de décision actionnable

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/migrations/Version20260403000000.php

@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+final class Version20260403000000 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Ajout eta_hours sur impact_score — horizon prévu d\'impact côtier';
+    }
+
+    public function up(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE impact_score ADD COLUMN eta_hours INT DEFAULT NULL');
+    }
+
+    public function down(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE impact_score DROP COLUMN IF EXISTS eta_hours');
+    }
+}