feat: restore sablog browse modes and clean imported HTML

Keep the public site readable after import (nbsp, highlighter, wrapping code, compact pager) and finish the admin extras already in this tree: sticky levels, preview, page cache, and live llms.txt.

Co-authored-by: Cursor <cursoragent@cursor.com>

resources/views/show.blade.php

@@ -14,6 +14,7 @@
         @if(session('error'))
             <div class="alert alert-error">{{ session('error') }}</div>
         @endif
+        @include('partials.post-preview-banner')
 
         <article class="post-full">
             @if(! empty($toc))
@@ -37,7 +38,11 @@
             @endif
             <h1 class="post-title">{{ $post->title }}</h1>
             <div class="post-meta">
-                <time datetime="{{ $post->published_at->toIso8601String() }}">{{ $post->published_at->format(blog_setting('normaltime', 'Y-m-d H:i')) }}</time>
+                @if($post->published_at)
+                    <time datetime="{{ $post->published_at->toIso8601String() }}">{{ $post->published_at->format(blog_setting('normaltime', 'Y-m-d H:i')) }}</time>
+                @else
+                    <span>未发布</span>
+                @endif
                 @if($post->author)<span>· {{ $post->author->name }}</span>@endif
                 @if($post->category)
                     <span>· <a href="{{ route('category.show', $post->category->id) }}">{{ $post->category->name }}</a></span>