[Adapters] lowStock reports digital and soft-deleted products that can never clear

[vedanshujain]

ReportingStore.lowStock is a bare scan of the inventory table:

selectFrom("inventory").select(["sku","on_hand"]).where("on_hand","<=",threshold)

(packages/store-postgres/src/kysely-reporting-store.ts:148-157). No join to product_commerce,
so there is no deleted_at filter and no product_kind filter. The default threshold is 5
(packages/domain/src/ports/settings-store.ts:39).

Why this is now worse

PR 1a establishes the invariant "a product with a SKU has an inventory row", seeding a row at 0
on both write paths. So every SKU'd product now appears in the low-stock report at 0 until it is
stocked, where previously only products that had been explicitly seeded appeared at all.

Two categories can never clear:

• Digital products. They hold no stock by design — nothing ever restocks them — so a digital
  SKU sits in the low-stock report permanently. product_kind lives on product_commerce, which
  this query never joins.
• Soft-deleted products. softDelete sets deleted_at on product_commerce and retains the
  row; the inventory row is untouched and keeps being reported.

The result is a report that a merchant learns to ignore, which is the failure mode a low-stock
alert can least afford.

Suggested direction

Join product_commerce and filter to deleted_at is null and product_kind = 'physical'. Needs
cases on both dialects and a decision on whether an inventory row with no matching
product_commerce row (possible after a SKU rename — see the SKU-rename stranding issue) should
be reported or hidden.

Deliberately not fixed in PR 1a: it is an [Adapters] + reporting-contract change, and 1a's
scope is the seeding invariant.