feat(overview): thread premium_usd through model.Lot + report read path

Add PremiumUSD to model.Lot and copy it in Resolve(), mirroring how the
Category/Subcategory/Trophy taxonomy fields are threaded. Also add premium_usd
to the ResolveDataset lots SELECT/Scan so the resolved dataset (and thus the
/api/summary report the Overview stack table consumes) actually carries it —
the scout's model-only prediction was necessary but insufficient; the read
query that feeds the report had to carry premium too. Premium is a display
memo (a component of basis), never summed into any melt/market total.

Extends TestResolve with a case asserting PremiumUSD threads through and does
not alter basis. Sell/split path (splitLot) untouched.

Refs: om-0pqe

Author: tompscanlan

internal/model/model.go

@@ -87,6 +87,7 @@ type Lot struct {
 	FaceValueUSD float64 `json:"face_value_usd"`
 	Acquired     string  `json:"acquired"`
 	Source       string  `json:"source"`
+	PremiumUSD   float64 `json:"premium_usd,omitempty"` // paid over melt at acquisition; a component of basis, display-only
 	Category     string  `json:"category,omitempty"`    // CRH find taxonomy (ADR-006)
 	Subcategory  string  `json:"subcategory,omitempty"` // CRH find taxonomy (ADR-006)
 	Trophy       bool    `json:"trophy,omitempty"`
@@ -117,6 +118,7 @@ func Resolve(h Holding, t ItemType) Lot {
 		FaceValueUSD: h.FaceValueUSD,
 		Acquired:     h.Acquired,
 		Source:       h.Source,
+		PremiumUSD:   h.PremiumUSD,
 		Category:     h.Category,
 		Subcategory:  h.Subcategory,
 		Trophy:       h.Trophy,

internal/model/model_test.go

@@ -46,3 +46,27 @@ func TestResolveUsesGrossWeightPurityAndUnit(t *testing.T) {
 		t.Fatalf("FineOzEach = %v, want %v", got, want)
 	}
 }
+
+// PremiumUSD is a display memo (paid over melt at acquisition), a component of
+// basis. It must thread from Holding through Resolve into the flat Lot so calc/UI
+// (the Overview stack table) can surface it — mirroring the taxonomy fields.
+func TestResolveThreadsPremiumUSD(t *testing.T) {
+	h := Holding{
+		ID:         1,
+		ItemTypeID: 1,
+		Qty:        1,
+		BasisUSD:   1512,
+		PremiumUSD: 62,
+		Acquired:   "2026-07-02",
+		Source:     "test",
+	}
+	itemType := ItemType{ID: 1, Name: "1 oz Gold Eagle", Metal: "gold", Fineness: ".9167", FineOzEach: 1}
+	lot := Resolve(h, itemType)
+	if got, want := lot.PremiumUSD, 62.0; got != want {
+		t.Fatalf("PremiumUSD = %v, want %v", got, want)
+	}
+	// Sanity: premium is a memo, not folded into basis by Resolve.
+	if got, want := lot.BasisUSD, 1512.0; got != want {
+		t.Fatalf("BasisUSD = %v, want %v (premium must not alter basis)", got, want)
+	}
+}

internal/store/data.go

@@ -284,7 +284,7 @@ func (s *Store) ResolveDataset() (model.Dataset, error) {
 	// holdings -> resolved lots
 	rows, err = s.db.Query(
 		`SELECT id, item_type_id, roll_txn_id, activity, qty, gross_weight, purity, weight_unit, basis_usd,
-		   face_value_usd, acquired, source, category, subcategory, trophy
+		   premium_usd, face_value_usd, acquired, source, category, subcategory, trophy
 		 FROM lots WHERE disposed IS NULL OR disposed = '' ORDER BY id`)
 	if err != nil {
 		return d, fmt.Errorf("load lots: %w", err)
@@ -295,7 +295,7 @@ func (s *Store) ResolveDataset() (model.Dataset, error) {
 		var source, cat, subcat, wu sql.NullString
 		var trophy int64
 		if err := rows.Scan(&h.ID, &h.ItemTypeID, &rtid, &h.Activity, &h.Qty, &h.GrossWeight,
-			&h.Purity, &wu, &h.BasisUSD, &h.FaceValueUSD, &h.Acquired, &source, &cat, &subcat, &trophy); err != nil {
+			&h.Purity, &wu, &h.BasisUSD, &h.PremiumUSD, &h.FaceValueUSD, &h.Acquired, &source, &cat, &subcat, &trophy); err != nil {
 			rows.Close()
 			return d, err
 		}