-[PM-27123] Update Signals and Update Estimated Tax and Credit Logic (#17055)

* billing(fix): update signals and update estimated tax and credit logic

* fix(billing): update with claude feedback and expose total observable

libs/pricing/src/components/cart-summary/cart-summary.component.ts

@@ -1,5 +1,6 @@
 import { CurrencyPipe } from "@angular/common";
 import { Component, computed, input, signal } from "@angular/core";
+import { toObservable } from "@angular/core/rxjs-interop";
 
 import { TypographyModule, IconButtonModule } from "@bitwarden/components";
 import { I18nPipe } from "@bitwarden/ui-common";
@@ -71,6 +72,11 @@ export class CartSummaryComponent {
    */
   readonly total = computed<number>(() => this.getTotalCost());
 
+  /**
+   * Observable of computed total value
+   */
+  readonly total$ = toObservable(this.total);
+
   /**
    * Toggles the expanded/collapsed state of the cart items
    */