Basic API consumption support and refactored UI to use material (#1)

Co-authored-by: Joe Arndt <jmarndt@users.noreply.github.com>
Reviewed-on: #1

src/app/services/category.service.ts

@@ -0,0 +1,24 @@
+import { Injectable, signal } from '@angular/core';
+import { HttpService } from './http.service';
+
+@Injectable({
+  providedIn: 'root'
+})
+export class CategoryService {
+  private internalCategories = signal<Category[]>([]);
+  public readonly categories = this.internalCategories.asReadonly();
+  public readonly categoryPath = 'http://localhost:3000/common-cents/categories';
+
+  public constructor(private readonly http: HttpService) {
+    void this.fetchCategories();
+  }
+
+  public async fetchCategories(): Promise<void> {
+    this.internalCategories.set(await this.http.get<Category[]>(this.categoryPath));
+  }
+}
+
+export interface Category {
+  id: string;
+  name: string;
+}