Add products, inventory units, stock receipts, and price history

- product table (catalog definition, no cost column — cost tracked
  per receipt/unit)
- inventory_unit table (serialized items with serial number,
  condition, status)
- stock_receipt table (FIFO cost tracking — records every stock
  receive event with cost_per_unit, supplier, date)
- price_history table (logs every retail price change for margin
  analysis over time)
- product_supplier join table (many-to-many, tracks supplier SKU
  and preferred supplier)
- Full CRUD routes + search (name, SKU, UPC, brand)
- Inventory unit routes nested under products
- Price changes auto-logged on product update
- 33 tests passing

packages/backend/src/services/product.service.ts

@@ -0,0 +1,157 @@
+import { eq, and, or, ilike } from 'drizzle-orm'
+import type { PostgresJsDatabase } from 'drizzle-orm/postgres-js'
+import { products, inventoryUnits, priceHistory } from '../db/schema/inventory.js'
+import type {
+  ProductCreateInput,
+  ProductUpdateInput,
+  InventoryUnitCreateInput,
+  InventoryUnitUpdateInput,
+} from '@forte/shared/schemas'
+
+export const ProductService = {
+  async create(db: PostgresJsDatabase, companyId: string, input: ProductCreateInput) {
+    const [product] = await db
+      .insert(products)
+      .values({
+        companyId,
+        ...input,
+        price: input.price?.toString(),
+        minPrice: input.minPrice?.toString(),
+        rentalRateMonthly: input.rentalRateMonthly?.toString(),
+      })
+      .returning()
+    return product
+  },
+
+  async getById(db: PostgresJsDatabase, companyId: string, id: string) {
+    const [product] = await db
+      .select()
+      .from(products)
+      .where(and(eq(products.id, id), eq(products.companyId, companyId)))
+      .limit(1)
+    return product ?? null
+  },
+
+  async list(db: PostgresJsDatabase, companyId: string) {
+    return db
+      .select()
+      .from(products)
+      .where(and(eq(products.companyId, companyId), eq(products.isActive, true)))
+      .limit(100)
+  },
+
+  async search(db: PostgresJsDatabase, companyId: string, query: string) {
+    const pattern = `%${query}%`
+    return db
+      .select()
+      .from(products)
+      .where(
+        and(
+          eq(products.companyId, companyId),
+          eq(products.isActive, true),
+          or(
+            ilike(products.name, pattern),
+            ilike(products.sku, pattern),
+            ilike(products.upc, pattern),
+            ilike(products.brand, pattern),
+          ),
+        ),
+      )
+      .limit(50)
+  },
+
+  async update(db: PostgresJsDatabase, companyId: string, id: string, input: ProductUpdateInput, changedBy?: string) {
+    // Log price changes before updating
+    if (input.price !== undefined || input.minPrice !== undefined) {
+      const existing = await this.getById(db, companyId, id)
+      if (existing) {
+        await db.insert(priceHistory).values({
+          productId: id,
+          companyId,
+          previousPrice: existing.price,
+          newPrice: input.price?.toString() ?? existing.price ?? '0',
+          previousMinPrice: existing.minPrice,
+          newMinPrice: input.minPrice?.toString() ?? existing.minPrice,
+          changedBy,
+        })
+      }
+    }
+
+    const updates: Record<string, unknown> = { ...input, updatedAt: new Date() }
+    if (input.price !== undefined) updates.price = input.price.toString()
+    if (input.minPrice !== undefined) updates.minPrice = input.minPrice.toString()
+    if (input.rentalRateMonthly !== undefined)
+      updates.rentalRateMonthly = input.rentalRateMonthly.toString()
+
+    const [product] = await db
+      .update(products)
+      .set(updates)
+      .where(and(eq(products.id, id), eq(products.companyId, companyId)))
+      .returning()
+    return product ?? null
+  },
+
+  async softDelete(db: PostgresJsDatabase, companyId: string, id: string) {
+    const [product] = await db
+      .update(products)
+      .set({ isActive: false, updatedAt: new Date() })
+      .where(and(eq(products.id, id), eq(products.companyId, companyId)))
+      .returning()
+    return product ?? null
+  },
+}
+
+export const InventoryUnitService = {
+  async create(db: PostgresJsDatabase, companyId: string, input: InventoryUnitCreateInput) {
+    const [unit] = await db
+      .insert(inventoryUnits)
+      .values({
+        companyId,
+        productId: input.productId,
+        locationId: input.locationId,
+        serialNumber: input.serialNumber,
+        condition: input.condition,
+        status: input.status,
+        purchaseDate: input.purchaseDate,
+        purchaseCost: input.purchaseCost?.toString(),
+        notes: input.notes,
+      })
+      .returning()
+    return unit
+  },
+
+  async getById(db: PostgresJsDatabase, companyId: string, id: string) {
+    const [unit] = await db
+      .select()
+      .from(inventoryUnits)
+      .where(and(eq(inventoryUnits.id, id), eq(inventoryUnits.companyId, companyId)))
+      .limit(1)
+    return unit ?? null
+  },
+
+  async listByProduct(db: PostgresJsDatabase, companyId: string, productId: string) {
+    return db
+      .select()
+      .from(inventoryUnits)
+      .where(
+        and(eq(inventoryUnits.companyId, companyId), eq(inventoryUnits.productId, productId)),
+      )
+  },
+
+  async update(
+    db: PostgresJsDatabase,
+    companyId: string,
+    id: string,
+    input: InventoryUnitUpdateInput,
+  ) {
+    const updates: Record<string, unknown> = { ...input }
+    if (input.purchaseCost !== undefined) updates.purchaseCost = input.purchaseCost.toString()
+
+    const [unit] = await db
+      .update(inventoryUnits)
+      .set(updates)
+      .where(and(eq(inventoryUnits.id, id), eq(inventoryUnits.companyId, companyId)))
+      .returning()
+    return unit ?? null
+  },
+}