feat: post cover filter + admin AI cover action, restyle page-cache admin

- 抽 CoverGenerator 服务（covers:generate 与后台共用），内部强制同步产出 card 转换
- 文章列表：新增封面状态图标列、「有/无封面/完全无图」筛选、行内「生成封面」AI 操作
- 页面缓存：统计改为原生 StatsOverviewWidget（缓存页数/总大小/命中率/时长），
  缓存明细表重排（表头、悬停、URL 截断、图标删除按钮、空状态）

app/Filament/Resources/Posts/Tables/PostsTable.php

@@ -4,17 +4,21 @@ declare(strict_types=1);
 
 namespace App\Filament\Resources\Posts\Tables;
 
+use App\Blog\Services\CoverGenerator;
 use App\Models\Post;
 use Filament\Actions\Action;
 use Filament\Actions\BulkActionGroup;
 use Filament\Actions\DeleteBulkAction;
 use Filament\Actions\EditAction;
 use Filament\Actions\ViewAction;
+use Filament\Notifications\Notification;
 use Filament\Support\Enums\Width;
+use Filament\Tables\Columns\IconColumn;
 use Filament\Tables\Columns\TextColumn;
 use Filament\Tables\Enums\FiltersLayout;
 use Filament\Tables\Filters\SelectFilter;
 use Filament\Tables\Table;
+use Illuminate\Database\Eloquent\Builder;
 
 class PostsTable
 {
@@ -46,6 +50,16 @@ class PostsTable
                         'draft' => 'warning',
                         default => 'gray',
                     }),
+                IconColumn::make('cover_state')
+                    ->label('封面')
+                    ->boolean()
+                    ->trueIcon('heroicon-o-photo')
+                    ->falseIcon('heroicon-o-x-mark')
+                    ->trueColor('success')
+                    ->falseColor('gray')
+                    ->state(fn (Post $record): bool => $record->coverImageUrl() !== null)
+                    ->tooltip(fn (Post $record): string => $record->coverImageUrl() !== null ? '已有封面' : '无封面，可用「生成封面」AI 补一张')
+                    ->toggleable(),
                 TextColumn::make('sticky_level')
                     ->label('置顶')
                     ->badge()
@@ -90,10 +104,50 @@ class PostsTable
                 SelectFilter::make('sticky_level')
                     ->label('置顶')
                     ->options(Post::stickyLevelOptions()),
+                SelectFilter::make('cover_status')
+                    ->label('封面')
+                    ->options([
+                        'with' => '有封面',
+                        'without' => '无封面',
+                        'no_image' => '完全无图（正文/附件也没有）',
+                    ])
+                    ->query(fn (Builder $query, array $data): Builder => match ($data['value'] ?? null) {
+                        'with' => $query->where(fn (Builder $q) => $q
+                            ->whereNotNull('cover_media_id')
+                            ->orWhereHas('media', fn (Builder $m) => $m->where('collection_name', 'cover'))),
+                        'without' => $query
+                            ->whereNull('cover_media_id')
+                            ->whereDoesntHave('media', fn (Builder $m) => $m->where('collection_name', 'cover')),
+                        'no_image' => $query
+                            ->whereNull('cover_media_id')
+                            ->whereDoesntHave('media', fn (Builder $m) => $m->where(fn (Builder $x) => $x
+                                ->where('collection_name', 'cover')
+                                ->orWhere(fn (Builder $y) => $y
+                                    ->where('collection_name', 'attachments')
+                                    ->where('mime_type', 'like', 'image/%'))))
+                            ->where('content', 'not like', '%<img%')
+                            ->where('content', 'not like', '%](http%'),
+                        default => $query,
+                    }),
             ], FiltersLayout::AboveContent)
             ->filtersFormColumns(3)
             ->filtersFormWidth(Width::ThreeExtraLarge)
             ->recordActions([
+                Action::make('generateCover')
+                    ->label('生成封面')
+                    ->icon('heroicon-o-photo')
+                    ->color('gray')
+                    ->requiresConfirmation()
+                    ->modalHeading('AI 生成封面')
+                    ->modalDescription(fn (Post $record): string => "根据《{$record->title}》的标题和摘要生成一张封面图，约需 20 秒，请耐心等待。")
+                    ->action(function (Post $record): void {
+                        try {
+                            app(CoverGenerator::class)->generateFor($record);
+                            Notification::make()->title('封面已生成')->success()->send();
+                        } catch (\Throwable $e) {
+                            Notification::make()->title('生成失败')->body($e->getMessage())->danger()->send();
+                        }
+                    }),
                 Action::make('preview')
                     ->label('预览')
                     ->url(fn (Post $record): string => $record->url)