User-supplied asset ids; brand on product; strain is the name

Four UX changes after using the rework for a bit:

1. Asset ids are 6-digit numbers from a roll of physical labels — server
   no longer generates them. POST /api/inventory requires assetId; the
   add-inventory form has a digits-only input that auto-focuses on entry.
2. Strain and product name are the same thing. Drop products.name; the
   strain's name supplies the display. Product creation just asks for
   "Name (strain)" and matches/creates a strain by that name.
3. Brand moves from inventory_items to products. SKUs are brand-specific,
   so all instances of a product share the brand. Brand selector lives
   on the product create/edit form, not the per-instance form.
4. Scanning an unknown SKU on the add-inventory step now opens the
   create-product subform with the SKU prefilled — one less click.

Migration: detect prior shape (products.name column present) and rename
products/inventory_items/audits to *_v1 archives, recreate empty.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/components/ProductDetail.tsx

@@ -46,7 +46,7 @@ export function ProductDetail({
     ["Asset id", <span className="mono">{item.assetId}</span>],
     ["SKU", <span className="mono">{item.sku}</span>],
     ["Type", `${item.type} · ${item.kind}`],
-    ["Strain", item.strainName ?? <span style={{ color: "var(--ink-3)" }}>Unlinked</span>],
+    ["Strain", item.name],
     ["Brand", helpers.brandName(data, item.brandId)],
     ["Shop", helpers.shopName(data, item.shopId)],
     ["Total cannabinoids", `${item.totalCannabinoids.toFixed(1)}%`],