fix(machine): production hardware fixes for Douro cash-out

- Fix cassette denominations: Douro uses Q100/Q200, not Q20
- Add hal:get-inventory IPC so renderer can read HAL cassette inventory
- Add balance fetch/display to HAL+IPC init path and idle screen
- Enable/disable bill validator via watch on nested state transitions
- Pass fiatCode to state machine context (was hardcoded to USD)
- Preserve currency across state machine resetContext
- Add CANCEL handler to dispenseError state (was stuck)
- Fix remaining hardcoded $ symbols in CashInView

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/machine/electron/main.ts

@@ -214,6 +214,11 @@ ipcMain.handle('hal:reject-bill', () => {
   }
 })
 
+ipcMain.handle('hal:get-inventory', () => {
+  if (!halInstance) return {}
+  return halInstance.getInventory()
+})
+
 ipcMain.handle('hal:cleanup', async () => {
   if (halInstance) {
     await halInstance.cleanup()