fix(composant) : scaffold skeleton slots on creation + explicit unique constraint errors

- Add ComposantProcessor: initializes piece/product/subcomponent slots
  from ModelType skeleton requirements when a composant is created
- UniqueConstraintSubscriber: priority 256, French error messages,
  constraint name detection for specific feedback
- Migration: scaffold missing slots for existing composants in prod

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

migrations/Version20260323100000.php

@@ -0,0 +1,91 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+/**
+ * Scaffold missing composant slots for existing composants that have
+ * a typeComposant with skeleton requirements but no corresponding slots.
+ */
+final class Version20260323100000 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Scaffold missing composant slots from skeleton requirements for existing composants';
+    }
+
+    public function up(Schema $schema): void
+    {
+        // Piece slots
+        $this->addSql(<<<'SQL'
+                INSERT INTO composant_piece_slots (id, "composantid", "typepieceid", quantity, position, "createdat", "updatedat")
+                SELECT
+                  'cl' || substr(md5(random()::text || clock_timestamp()::text || spr.id), 1, 24),
+                  c.id,
+                  spr."typepieceid",
+                  1,
+                  spr.position,
+                  NOW(),
+                  NOW()
+                FROM composants c
+                JOIN skeleton_piece_requirements spr ON spr."modeltypeid" = c."typecomposantid"
+                WHERE c."typecomposantid" IS NOT NULL
+                  AND NOT EXISTS (
+                    SELECT 1 FROM composant_piece_slots cps
+                    WHERE cps."composantid" = c.id AND cps."typepieceid" = spr."typepieceid"
+                  )
+            SQL);
+
+        // Product slots
+        $this->addSql(<<<'SQL'
+                INSERT INTO composant_product_slots (id, "composantid", "typeproductid", "familycode", position, "createdat", "updatedat")
+                SELECT
+                  'cl' || substr(md5(random()::text || clock_timestamp()::text || spr.id), 1, 24),
+                  c.id,
+                  spr."typeproductid",
+                  spr."familycode",
+                  spr.position,
+                  NOW(),
+                  NOW()
+                FROM composants c
+                JOIN skeleton_product_requirements spr ON spr."modeltypeid" = c."typecomposantid"
+                WHERE c."typecomposantid" IS NOT NULL
+                  AND NOT EXISTS (
+                    SELECT 1 FROM composant_product_slots cps
+                    WHERE cps."composantid" = c.id AND cps."typeproductid" = spr."typeproductid"
+                  )
+            SQL);
+
+        // Subcomponent slots
+        $this->addSql(<<<'SQL'
+                INSERT INTO composant_subcomponent_slots (id, "composantid", alias, "familycode", "typecomposantid", position, "createdat", "updatedat")
+                SELECT
+                  'cl' || substr(md5(random()::text || clock_timestamp()::text || spr.id), 1, 24),
+                  c.id,
+                  spr.alias,
+                  spr."familycode",
+                  spr."typecomposantid",
+                  spr.position,
+                  NOW(),
+                  NOW()
+                FROM composants c
+                JOIN skeleton_subcomponent_requirements spr ON spr."modeltypeid" = c."typecomposantid"
+                WHERE c."typecomposantid" IS NOT NULL
+                  AND NOT EXISTS (
+                    SELECT 1 FROM composant_subcomponent_slots css
+                    WHERE css."composantid" = c.id
+                      AND COALESCE(css."typecomposantid", '') = COALESCE(spr."typecomposantid", '')
+                      AND COALESCE(css.alias, '') = COALESCE(spr.alias, '')
+                  )
+            SQL);
+    }
+
+    public function down(Schema $schema): void
+    {
+        // No-op: slots created by this migration are valid data
+    }
+}