Frontend optimizations: SVG icons, remove updateFileIcons, unify rendering, scope translatePage

- Replace Font Awesome CDN with inline SVG system (icons.js + MutationObserver)
- Remove updateFileIcons() (~140 lines) - redundant with backend icon_class + MutationObserver
- Migrate favorites.js and recent.js to use shared ui.renderFolders/renderFiles (eliminate ~260 lines of duplicate rendering + per-item event listeners)
- Add view-mode aware click delegation for favorites/recent views
- Fix _createFileCard to apply icon_special_class
- Add translateElement(root) for scoped i18n translation
- Replace full-page translatePage() calls with scoped translateElement() or inline t()
- Remove redundant translatePage() calls in shared.js and auth.js
- Remove Alpine.js from Service Worker cache

static/admin.html

@@ -6,7 +6,7 @@
 <title>OxiCloud — Admin Panel</title>
 <!-- Apply saved theme immediately to prevent flash of light mode -->
 <script>if(localStorage.getItem('oxicloud_theme')==='dark')document.documentElement.setAttribute('data-theme','dark');</script>
-<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.0.0-beta3/css/all.min.css">
+<script src="/js/icons.js" defer></script>
 <style>
 *{box-sizing:border-box;margin:0;padding:0;font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,Oxygen,Ubuntu,Cantarell,'Open Sans','Helvetica Neue',sans-serif}
 body{background:#f5f7fa;color:#1e293b;min-height:100vh;display:flex;flex-direction:column}