feat(reference-auto) : add automatic reference generation for pieces

ModelType defines a formula with placeholders ({serie}{diametre}{type}).
ReferenceAutoGenerator resolves it from CustomFieldValues with trim+uppercase normalisation.
ReferenceAutoSubscriber (onFlush) recalculates on Piece/CFV insert/update/delete.

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

src/Entity/Piece.php

@@ -63,6 +63,10 @@ class Piece
     #[Groups(['piece:read'])]
     private ?string $reference = null;
 
+    #[ORM\Column(type: Types::STRING, length: 255, nullable: true)]
+    #[Groups(['piece:read'])]
+    private ?string $referenceAuto = null;
+
     #[ORM\Column(type: Types::TEXT, nullable: true)]
     #[Groups(['piece:read'])]
     private ?string $description = null;
@@ -179,6 +183,21 @@ class Piece
         return $this;
     }
 
+    public function getReferenceAuto(): ?string
+    {
+        return $this->referenceAuto;
+    }
+
+    /**
+     * @internal used by ReferenceAutoSubscriber only — not part of the public API
+     */
+    public function setReferenceAuto(?string $referenceAuto): static
+    {
+        $this->referenceAuto = $referenceAuto;
+
+        return $this;
+    }
+
     public function getDescription(): ?string
     {
         return $this->description;