Add user auth, cart, checkout and personal account for guests and registered users

internal/handlers/templates/shop_header.html

@@ -0,0 +1,26 @@
+{{define "shop_header"}}
+<header class="header">
+    <div class="container header__inner">
+        <a href="/" class="logo">
+            <span class="logo__icon">◆</span>
+            <span class="logo__text">Shop</span>
+        </a>
+        <nav class="nav">
+            <a href="/#catalog" class="nav__link">Каталог</a>
+            <a href="/#categories" class="nav__link">Категории</a>
+            <a href="/#delivery" class="nav__link">Доставка</a>
+        </nav>
+        <div class="header__actions">
+            {{if .User}}
+            <a href="/account" class="btn btn--ghost btn--sm">👤 {{.User.Name}}</a>
+            {{else}}
+            <a href="/login" class="btn btn--ghost btn--sm">Войти</a>
+            <a href="/register" class="btn btn--ghost btn--sm">Регистрация</a>
+            {{end}}
+            <a href="/cart" class="btn btn--primary btn--sm">
+                🛒 Корзина{{if .CartCount}} ({{.CartCount}}){{end}}
+            </a>
+        </div>
+    </div>
+</header>
+{{end}}