feat(holdings): add premium_usd column to the Holdings grid

Mirror the face_value_usd money column across all five grid touch points:
FlatHolding gains premium_usd, a "Premium $" column sits next to Basis $/Face $,
load() maps premium_usd in, toHolding() writes it back, and blank() defaults it.
toHolding() writing premium_usd is the critical line — without it the API's bare
json.Unmarshal zeroes the field on every save. Because premium_usd is now a
required FlatHolding field, the three Do-tab quick-entry workflows that build a
FlatHolding (NewBullion, LoggedFinds, Reconcile) default it to 0.

Refs: om-0pqe

Author: tompscanlan

web/app/src/lib/components/workflows/LoggedFinds.svelte

@@ -160,6 +160,7 @@
           fine_oz_each: Number(f.fineOz) || 0,
           qty: Number(f.qty) || 0,
           basis_usd: faceTotal,
+          premium_usd: 0, // CRH finds carry no premium over melt (acquired at face)
           face_value_usd: faceTotal,
           acquired: chosenDate || today(),
           source: chosenBank.trim(),

web/app/src/lib/components/workflows/NewBullion.svelte

@@ -87,6 +87,7 @@
         fine_oz_each: Number(fineOz) || 0,
         qty: Number(qty) || 0,
         basis_usd: Number(basis) || 0,
+        premium_usd: 0, // not collected in the quick-entry form; editable in the Holdings grid
         face_value_usd: 0,
         acquired: acquired || today(),
         source: source.trim(),

web/app/src/lib/components/workflows/Reconcile.svelte

@@ -134,6 +134,7 @@
         fine_oz_each: Number(fFineOz) || 0,
         qty: Number(fQty) || 0,
         basis_usd: faceTotal,
+        premium_usd: 0, // CRH finds carry no premium over melt (acquired at face)
         face_value_usd: faceTotal,
         acquired: today(),
         source: fBox ? (buys.find((b) => String(b.id) === fBox)?.bank ?? '') : '',

web/app/src/lib/grids.ts

@@ -115,6 +115,7 @@ export interface FlatHolding {
   weight_unit?: string
   qty: number
   basis_usd: number
+  premium_usd: number
   face_value_usd: number
   acquired: string
   source: string
@@ -162,6 +163,7 @@ function toHolding(row: Omit<FlatHolding, 'id'>, item_type_id: number): Omit<Hol
     purity: row.purity,
     weight_unit: row.weight_unit,
     basis_usd: Number(row.basis_usd) || 0,
+    premium_usd: Number(row.premium_usd) || 0,
     face_value_usd: Number(row.face_value_usd) || 0,
     acquired: row.acquired,
     source: row.source,
@@ -197,6 +199,7 @@ export const holdingsGrid: GridConfig<FlatHolding> = {
     { accessorKey: 'weight_unit', header: 'Unit', meta: { editor: 'select', options: ['ozt', 'g', 'kg'], width: '90px' } },
     { accessorKey: 'qty', header: 'Qty', meta: { editor: 'number', step: 1, align: 'right', width: '80px' } },
     { accessorKey: 'basis_usd', header: 'Basis $', meta: { editor: 'number', step: 0.01, align: 'right', width: '110px' } },
+    { accessorKey: 'premium_usd', header: 'Premium $', meta: { editor: 'number', step: 0.01, align: 'right', width: '110px' } },
     { accessorKey: 'face_value_usd', header: 'Face $', meta: { editor: 'number', step: 0.01, align: 'right', width: '100px' } },
     { accessorKey: 'acquired', header: 'Acquired', meta: { editor: 'date', width: '150px' } },
     { accessorKey: 'source', header: 'Source', meta: { editor: 'autocomplete', placeholder: 'APMEX', suggestions: () => holdingSources } },
@@ -238,6 +241,7 @@ export const holdingsGrid: GridConfig<FlatHolding> = {
         weight_unit: h.weight_unit,
         qty: h.qty,
         basis_usd: h.basis_usd,
+        premium_usd: h.premium_usd ?? 0,
         face_value_usd: h.face_value_usd,
         acquired: h.acquired,
         source: h.source,
@@ -268,6 +272,7 @@ export const holdingsGrid: GridConfig<FlatHolding> = {
     weight_unit: 'ozt',
     qty: 1,
     basis_usd: 0,
+    premium_usd: 0,
     face_value_usd: 0,
     acquired: today(),
     source: '',