added header and footer

Co-authored-by: Copilot <copilot@github.com>

src/app/site-header/site-header.ts

@@ -0,0 +1,14 @@
+import { Component, signal } from '@angular/core';
+import { RouterLink } from '@angular/router';
+
+@Component({
+  selector: 'app-site-header',
+  imports: [RouterLink],
+  templateUrl: './site-header.html',
+  styleUrl: './site-header.scss'
+})
+export class SiteHeader {
+  menuOpen = signal(false);
+  toggleMenu(): void { this.menuOpen.update(v => !v); }
+  closeMenu(): void { this.menuOpen.set(false); }
+}