feat: add acquisition API foundation

Add acquisition persistence, cost-basis calculation, seller-scoped admin routes, contracts, validation, migration, and focused application/HTTP tests.

packages/contracts/acquisition.js

@@ -0,0 +1,24 @@
+function toIsoString(value) {
+  return value instanceof Date ? value.toISOString() : value;
+}
+
+export function toAdminAcquisitionDto(acquisition) {
+  return {
+    id: acquisition.id,
+    inventoryItemId: acquisition.inventoryItemId,
+    method: acquisition.method,
+    costMinor: acquisition.costMinor,
+    currency: acquisition.currency,
+    date: acquisition.date ?? null,
+    source: acquisition.source ?? null,
+    location: acquisition.location ?? null,
+    shippingMinor: acquisition.shippingMinor,
+    taxMinor: acquisition.taxMinor,
+    otherFeesMinor: acquisition.otherFeesMinor,
+    estimatedTradeValueMinor: acquisition.estimatedTradeValueMinor,
+    costBasisMinor: acquisition.costBasisMinor ?? null,
+    notes: acquisition.notes ?? null,
+    createdAt: toIsoString(acquisition.createdAt),
+    updatedAt: toIsoString(acquisition.updatedAt),
+  };
+}

packages/contracts/package.json

@@ -4,6 +4,7 @@
   "type": "module",
   "exports": {
     "./auth": "./auth.js",
+    "./acquisition": "./acquisition.js",
     "./inventory": "./inventory.js",
     "./image": "./image.js",
     "./listing": "./listing.js",