feat: add favicon (SVG shopping-bag logo + ICO fallback)

Orange #FF5500 rounded-square with shopping-bag icon matching the
sidebar logo. Includes SVG (modern), ICO (16+32px, legacy), and
apple-touch-icon PNG.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/templates/login.html

@@ -4,6 +4,9 @@
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>Вход — Мои Товары</title>
+  <link rel="icon" href="/static/favicon.ico" sizes="16x16 32x32" type="image/x-icon">
+  <link rel="icon" href="/static/favicon.svg" type="image/svg+xml">
+  <link rel="apple-touch-icon" href="/static/favicon-32.png">
   <link rel="preconnect" href="https://fonts.googleapis.com">
   <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
   <link href="https://fonts.googleapis.com/css2?family=Golos+Text:wght@400;500;600;700;800&family=JetBrains+Mono:wght@400;500&display=swap" rel="stylesheet">