Add bulk spool addition and stock spools

Add Quick Add mode to the spool form for simplified entry (material +
color + weight only), and a quantity field (1-100) for creating multiple
identical spools at once. Stock spools (no slicer profile) are computed
rather than stored — any spool without slicer_filament shows an amber
"Stock" badge. New filter chips (All/Stock/Configured) on the inventory
page. Backend bulk endpoint creates N spools in one transaction.

Backend:
- SpoolBulkCreate schema with quantity validation (1-100)
- POST /inventory/spools/bulk endpoint

Frontend:
- Quick Add toggle in SpoolFormModal (create mode only)
- Quantity field in FilamentSection (both modes)
- bulkCreateSpools API method and bulkCreateMutation
- Stock column (hidden by default) and stock filter chips
- Inline error rendering moved into FilamentSection
- CellCtx extended with t() for translatable cell content

Tests:
- 13 backend tests (schema validation + endpoint logic)
- 10 frontend tests (validateForm quickAdd + UI behavior)

i18n: 6 locales (en, de, fr, it, ja, pt-BR)
Docs: CHANGELOG, README, website features, wiki inventory

frontend/src/api/client.ts

@@ -3469,6 +3469,11 @@ export const api = {
       method: 'POST',
       body: JSON.stringify(data),
     }),
+  bulkCreateSpools: (data: Omit<InventorySpool, 'id' | 'archived_at' | 'created_at' | 'updated_at' | 'k_profiles'>, quantity: number) =>
+    request<InventorySpool[]>('/inventory/spools/bulk', {
+      method: 'POST',
+      body: JSON.stringify({ spool: data, quantity }),
+    }),
   updateSpool: (id: number, data: Partial<Omit<InventorySpool, 'id' | 'archived_at' | 'created_at' | 'updated_at' | 'k_profiles'>>) =>
     request<InventorySpool>(`/inventory/spools/${id}`, {
       method: 'PATCH',