List tax categories for the tenant

Story 4 AC-4.10.6. Returns the tenant's live tax categories (rows where `deleted_at IS NULL`) ordered by `code`. Envelope `{ items, total }`. Each item: `{ id, code, name, rate_bp, inclusive }`. Gated by `pos.catalog.read`.

curl -X GET "https://example.com/api/pos/v1/catalog/tax-categories"

{
  "items": [
    {
      "id": "018f4d9f-7b8a-7c2d-9a2d-1f8b92f6e401",
      "code": "STANDARD",
      "name": "PPN 11%",
      "rate_bp": 1100,
      "inclusive": true,
      "tax_kind": "ppn",
      "dpp_basis": "post_discount"
    }
  ],
  "total": 1
}