Add container weight tracking for weigh-based concentrate audits

Record the total weight of a jar (product + container) at acquisition so
audits can be done by simply re-weighing the sealed jar. The tare is
derived (containerWeight − productWeight), and the audit flow offers a
"Weigh container" toggle that auto-calculates remaining product from the
scale reading.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/types.ts

@@ -38,6 +38,7 @@ export interface InventoryItem {
   cbd: number;
   totalCannabinoids: number;
   weight: number;
+  containerWeight: number | null;
   lastAuditWeight: number | null;
   countOriginal: number;
   countLastAudit: number | null;
@@ -183,6 +184,10 @@ export const helpers = {
   typeConfig(id: string): TypeConfig {
     return TYPES.find((t) => t.id === id) ?? TYPES[0]!;
   },
+  tare(item: { containerWeight: number | null; weight: number }): number | null {
+    if (item.containerWeight == null) return null;
+    return item.containerWeight - item.weight;
+  },
   daysSince(iso: string | null, today = TODAY_STR): number {
     if (!iso) return Infinity;
     return Math.floor((+new Date(today) - +new Date(iso)) / 86_400_000);