refactor(model): split modelUtils.ts into 3 thematic modules (F5.1)

Split 1017 LOC monolith into:
- shared/model/componentStructure.ts (~590 LOC)
- shared/model/pieceProductStructure.ts (~155 LOC)
- shared/model/definitionOverrides.ts (~50 LOC)

Rewrite modelUtils.ts as 37 LOC barrel re-export for backward compat.
All 11 consumer files unchanged.

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

app/shared/model/definitionOverrides.ts

@@ -0,0 +1,49 @@
+import { uniqueConstructeurIds } from '../constructeurUtils'
+
+export interface DefinitionOverridePayload {
+  name?: string
+  reference?: string
+  constructeurIds?: string[]
+  prix?: number
+}
+
+export const sanitizeDefinitionOverrides = (definition: any): DefinitionOverridePayload | null => {
+  if (!definition || typeof definition !== 'object') {
+    return null
+  }
+
+  const payload: DefinitionOverridePayload = {}
+
+  if (typeof definition.name === 'string') {
+    const name = definition.name.trim()
+    if (name.length > 0) {
+      payload.name = name
+    }
+  }
+
+  if (typeof definition.reference === 'string') {
+    const reference = definition.reference.trim()
+    if (reference.length > 0) {
+      payload.reference = reference
+    }
+  }
+
+  const constructeurIds = uniqueConstructeurIds(
+    definition.constructeurIds,
+    definition.constructeurId,
+    definition.constructeur,
+    definition.constructeurs,
+  )
+  if (constructeurIds.length) {
+    payload.constructeurIds = constructeurIds
+  }
+
+  if (definition.prix !== undefined && definition.prix !== null && definition.prix !== '') {
+    const parsed = Number(definition.prix)
+    if (!Number.isNaN(parsed)) {
+      payload.prix = parsed
+    }
+  }
+
+  return Object.keys(payload).length ? payload : null
+}