docs: add JSDoc comments to ButtonsComponent

src/app/shared/components/buttons/btn-back/btn-back.component.ts

@@ -12,6 +12,9 @@ import { Location } from '@angular/common';
 export class BtnBackComponent {
   constructor(private location: Location) {}
 
+  /**
+   * Navigates back in the browser's history.
+   */
   backClicked() {
     this.location.back();
   }

src/app/shared/components/buttons/btn-close/btn-close.component.ts

@@ -13,6 +13,12 @@ export class BtnCloseComponent {
 
   constructor(private sharedService: SharedService) {}
 
+  /**
+   * Called when the close button is clicked.
+   * Sets isAnyDialogOpen to false and sets
+   * isEditContactDialogOpen and isNewContactDialogOpen
+   * to the value of isContactDialogOpen.
+   */
   closeClicked() {
     this.sharedService.isAnyDialogOpen = false;
     this.sharedService.isEditContactDialogOpen = this.isContactDialogOpen;