✨ feat(vscode): 看板顶部加筛选框，按标题 / 工单号 / PR 号过滤卡片

工单多了以后靠肉眼在四列里翻太慢。顶部输入框按空白分词逐词 AND 匹配
标题、工单号、PR 号，`#427` 与 `427` 等价，纯数字按包含匹配，记不全
编号也能搜到。筛选只收窄渲染，拖拽与依赖锁定仍按全量列表算；列头角标
在筛选时显示「可见 / 总数」。

vscode/webview-ui/src/components/KanbanColumn.tsx

@@ -9,12 +9,15 @@ import { Badge } from './ui/badge'
 interface KanbanColumnProps {
   column: IssueColumn
   issues: Issue[]
+  /** 该列未经筛选的卡片总数。与 `issues.length` 不等时角标显示「可见 / 总数」。 */
+  totalCount?: number
   children: ReactNode
   /** When provided, renders a + button in the header. Used for the todo column. */
   onCreate?: () => void
 }
 
-export function KanbanColumn({ column, issues, children, onCreate }: KanbanColumnProps) {
+export function KanbanColumn({ column, issues, totalCount, children, onCreate }: KanbanColumnProps) {
+  const filtered = totalCount !== undefined && totalCount !== issues.length
   const { setNodeRef, isOver } = useDroppable({ id: column })
 
   return (
@@ -31,7 +34,7 @@ export function KanbanColumn({ column, issues, children, onCreate }: KanbanColum
           {COLUMN_LABELS[column]}
         </span>
         <div className="flex items-center gap-1.5">
-          <Badge variant="outline">{issues.length}</Badge>
+          <Badge variant="outline">{filtered ? `${issues.length} / ${totalCount}` : issues.length}</Badge>
           {onCreate && (
             <button
               type="button"
@@ -49,7 +52,7 @@ export function KanbanColumn({ column, issues, children, onCreate }: KanbanColum
         {issues.length === 0
           ? (
               <div className="flex flex-1 items-center justify-center rounded-md border border-dashed border-[var(--vscode-foreground)] border-opacity-20 p-4 text-xs text-muted-foreground opacity-60">
-                拖到这里
+                {filtered ? '没有匹配的工单' : '拖到这里'}
               </div>
             )
           : (