feat(api): CRUD files/folders + upload multipart réels (scope owner, soft-delete, conteurs d'erreurs)

- repository.Resources (insert/list/get/soft-delete scoping owner_id, UNIQUE(parent_id,name) → NAME_CONFLICT) + Devices.Upsert au register
- service.Resources : DTOs {id,name,size,mimeType,folderId,createdAt,updatedAt}, upload → UPLOAD_DIR/<device>/<id>.<ext> (nettoyage si métadonnée échoue)
- handlers : files list/get/delete/upload + folders racines ; routes consolidées dans handlers.RegisterRoutes
- dbtest package : test DB jetée par repo (open+reset+migrate, skip si PG down) ; tests repository + handlers end-to-end (register→token→CRUD, scoping cross-device, FILE_TOO_LARGE, NAME_CONFLICT)
- docs: /devices persiste le device, layout UPLOAD_DIR par device, codes NAME_CONFLICT/SERVICE_UNAVAILABLE

backend/handlers/devices.go

@@ -25,6 +25,15 @@ func DevicesRegister(c *gin.Context) {
 		return
 	}
 
+	if Store == nil || Store.Repository == nil {
+		api.Error(c, 503, "SERVICE_UNAVAILABLE", "backend not initialized")
+		return
+	}
+	if err := Store.Repository.Devices.Upsert(req.DeviceID); err != nil {
+		api.Error(c, 500, "INTERNAL", "could not persist device")
+		return
+	}
+
 	token, err := Auth.Issue(req.DeviceID)
 	if err != nil {
 		api.Error(c, 500, "TOKEN_ERROR", "could not issue token")