feat: add pricing observation API

Add seller-owned pricing observation persistence, median market valuation calculation, admin routes, contracts, validation, migration, and focused tests.

packages/validation/package.json

@@ -10,6 +10,7 @@
     "./listing": "./listing.js",
     "./sale": "./sale.js",
     "./product": "./product.js"
+    ,"./pricing": "./pricing.js"
   },
   "dependencies": {
     "zod": "^4.1.8"

packages/validation/pricing.js

@@ -0,0 +1,13 @@
+import { z } from 'zod';
+
+export const createPricingObservationSchema = z.object({
+  productId: z.uuid(),
+  inventoryItemId: z.uuid(),
+  providerId: z.string().trim().min(1).max(100),
+  priceMinor: z.int().positive(),
+  currency: z.string().trim().regex(/^[A-Za-z]{3}$/).optional(),
+  sourceIdentifier: z.string().trim().min(1).max(255),
+  conditionId: z.uuid(),
+  sourceUrl: z.string().trim().url().optional(),
+  qualityScore: z.int().min(0).max(100).optional(),
+}).strict();