feat: add drawer cash in/out adjustments with balance reconciliation

- New drawer_adjustment table (type: cash_in/cash_out, amount, reason)
- POST/GET /drawer/:id/adjustments endpoints
- Drawer close calculation now includes adjustments: expected = opening + sales + cash_in - cash_out
- DrawerAdjustmentSchema for input validation
- 5 new tests (44 total POS tests passing)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/backend/src/db/schema/pos.ts

@@ -68,6 +68,8 @@ export const discounts = pgTable('discount', {
   updatedAt: timestamp('updated_at', { withTimezone: true }).notNull().defaultNow(),
 })
 
+export const adjustmentTypeEnum = pgEnum('adjustment_type', ['cash_in', 'cash_out'])
+
 export const drawerSessions = pgTable('drawer_session', {
   id: uuid('id').primaryKey().defaultRandom(),
   locationId: uuid('location_id').references(() => locations.id),
@@ -86,6 +88,20 @@ export const drawerSessions = pgTable('drawer_session', {
   closedAt: timestamp('closed_at', { withTimezone: true }),
 })
 
+export const drawerAdjustments = pgTable('drawer_adjustment', {
+  id: uuid('id').primaryKey().defaultRandom(),
+  drawerSessionId: uuid('drawer_session_id')
+    .notNull()
+    .references(() => drawerSessions.id),
+  type: adjustmentTypeEnum('type').notNull(),
+  amount: numeric('amount', { precision: 10, scale: 2 }).notNull(),
+  reason: text('reason').notNull(),
+  createdBy: uuid('created_by')
+    .notNull()
+    .references(() => users.id),
+  createdAt: timestamp('created_at', { withTimezone: true }).notNull().defaultNow(),
+})
+
 export const transactions = pgTable('transaction', {
   id: uuid('id').primaryKey().defaultRandom(),
   locationId: uuid('location_id').references(() => locations.id),