Chore: Upgrade to Angular v18

Chore: Upgrade to Python 3.12
Chore: Upgrade to psycopg3

bookie/src/app/settings/prefill-customer-discount.resolver.ts

@@ -0,0 +1,8 @@
+import { inject } from '@angular/core';
+import { ResolveFn } from '@angular/router';
+
+import { SettingsService } from './settings.service';
+
+export const prefillCustomerDiscountResolver: ResolveFn<boolean> = () => {
+  return inject(SettingsService).getPrefillCustomerDiscount();
+};