feat(web): componentize frontend and replace native delete confirm

- Split monolithic app.js/style.css into Alpine.js components (icons, store, fileSection, confirm)
- Add central Alpine.store('files') as single source of truth for file lists and actions
- Replace duplicated Inbox/Outbox markup with reusable fileSection component (props: dir, canShare)
- Add shared window.Icons module to remove duplicated inline SVGs
- Replace browser-native confirm() for file deletion with a styled, accessible modal dialog
- Split CSS into design tokens, base, and component layers; modernize visuals
- Update web.go embed and server static routes for the new component/style dirs

web/login.html

@@ -4,7 +4,9 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>yDropbox Login</title>
-    <link rel="stylesheet" href="/style.css">
+    <link rel="stylesheet" href="/styles/tokens.css">
+    <link rel="stylesheet" href="/styles/base.css">
+    <link rel="stylesheet" href="/styles/components.css">
 </head>
 <body>
     <div class="login-wrap">