feat: add pricing observation API

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

apps/api/src/infrastructure/database/schema.js

@@ -261,6 +261,34 @@ export const acquisitions = pgTable('acquisitions', {
   ...timestamps,
 });
 
+export const pricingObservations = pgTable('pricing_observations', {
+  id: uuid('id').defaultRandom().primaryKey(),
+  productId: uuid('product_id').notNull().references(() => products.id),
+  inventoryItemId: uuid('inventory_item_id').notNull().references(() => inventoryItems.id),
+  providerId: text('provider_id').notNull(),
+  priceMinor: integer('price_minor').notNull(),
+  currency: text('currency').notNull(),
+  sourceIdentifier: text('source_identifier').notNull(),
+  conditionId: uuid('condition_id').notNull().references(() => conditions.id),
+  sourceUrl: text('source_url'),
+  qualityScore: integer('quality_score'),
+  isOutlier: boolean('is_outlier').default(false).notNull(),
+  outlierReason: text('outlier_reason'),
+  observedAt: timestamp('observed_at', { withTimezone: true }).defaultNow().notNull(),
+  ...timestamps,
+}, (table) => [index('pricing_observations_inventory_item_id_index').on(table.inventoryItemId)]);
+
+export const marketValuations = pgTable('market_valuations', {
+  id: uuid('id').defaultRandom().primaryKey(),
+  inventoryItemId: uuid('inventory_item_id').notNull().references(() => inventoryItems.id),
+  valueMinor: integer('value_minor').notNull(),
+  currency: text('currency').notNull(),
+  strategy: text('strategy').notNull(),
+  confidence: text('confidence').notNull(),
+  sourceCount: integer('source_count').notNull(),
+  calculatedAt: timestamp('calculated_at', { withTimezone: true }).defaultNow().notNull(),
+});
+
 export const inventoryImages = pgTable(
   'inventory_images',
   {