feat: topbar legacy-sync button, card view mode with cover fallback, year/month/day archives, richer page cache admin, stylevar repeater editor

- topbar: Livewire LegacySyncButton next to 写文章 (moved from user menu)
- view modes: add 图文(card) grid with cover fallback chain (cover → attachment → first content image → placeholder); list mode now title-only compact
- archives: year/month/day index grid
- page cache admin: size + expiry columns, total size, cache policy note
- theme inject: stylevars switch from KeyValue to Repeater with multi-line HTML editing
- import: html_entity_decode for category/post-title/link/keywords/comment author

resources/views/livewire/legacy-sync-button.blade.php

@@ -0,0 +1,13 @@
+<div>
+    <x-filament::button
+        size="sm"
+        color="info"
+        icon="heroicon-o-arrow-path"
+        wire:click="run"
+        wire:loading.attr="disabled"
+        wire:confirm="将从旧 sablog 库增量导入文章/评论/标签等（幂等，不会产生重复），约需 1 分钟。确定开始？"
+    >
+        <span wire:loading.remove wire:target="run">同步旧站</span>
+        <span wire:loading wire:target="run">同步中…</span>
+    </x-filament::button>
+</div>