Enable adding a component, piece, or product to a machine by selecting
only the category (ModelType) without a specific entity. The link
displays a red "À remplir" badge; clicking it reopens the modal
pre-filled with the category so the user can associate an item later.
Backend: entity FKs made nullable on the 3 link tables, modelType FK
added, controller/audit/version/MCP normalization adapted for null
entities.
Frontend: modal accepts category-only confirm, page handles fill mode,
hierarchy builder creates pending nodes, display components show
clickable badge with event propagation through the full hierarchy.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Merges the full git history of Inventory_frontend into the monorepo
under frontend/. Removes the submodule in favor of a unified repo.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
