feat: named registers, X/Z reports, daily rollup, fix drawerSessionId

Registers:
- New register table with location association
- CRUD service + API routes (POST/GET/PATCH/DELETE /registers)
- Drawer sessions now link to a register via registerId
- Register ID persisted in localStorage per device

X/Z Reports:
- ReportService with getDrawerReport() (X or Z depending on session state)
- Z report auto-displayed on drawer close in the drawer dialog
- X report (Current Shift Report) button on open drawer view
- Report shows: sales summary, payment breakdown, discounts, cash accountability, adjustments

Daily Rollup:
- ReportService.getDailyReport() aggregates all sessions at a location for a date
- New /reports/daily endpoint with locationId + date params
- Frontend daily report page with date picker, location selector, session breakdown

Critical Fix:
- drawerSessionId is now populated on transactions when completing (was never set before)
- This enables accurate per-drawer reporting and cash accountability

Migration 0044: register table, drawer_session.register_id column

Tests: 14 new (register CRUD, drawer report X/Z, drawerSessionId population, daily rollup, register-drawer link)
Full suite: 367 passed

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

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

@@ -329,6 +329,7 @@ export const TransactionService = {
     if (txn.status !== 'pending') throw new ConflictError('Transaction is not pending')
 
     // Require an open drawer session at the transaction's location
+    let drawerSessionId: string | null = null
     if (txn.locationId) {
       const [openDrawer] = await db
         .select({ id: drawerSessions.id })
@@ -338,6 +339,7 @@ export const TransactionService = {
       if (!openDrawer) {
         throw new ValidationError('Cannot complete transaction without an open drawer at this location')
       }
+      drawerSessionId = openDrawer.id
     }
 
     // Validate cash payment (with optional nickel rounding)
@@ -399,6 +401,7 @@ export const TransactionService = {
           changeGiven,
           roundingAdjustment: roundingAdjustment.toString(),
           checkNumber: input.checkNumber,
+          drawerSessionId,
           completedAt: new Date(),
           updatedAt: new Date(),
         })