优化: 响应式布局走查修复(断点统一+窄屏适配)

- 统一断点: Dashboard/Ideas/Projects/ProjectDetail 的响应式断点
  从 900px 改为 768px,与 AppLayout/AppSidebar 对齐(消除中间区间挤压)
- filter-bar 全局加 flex-wrap:wrap(窄屏自动换行,Ideas/Tasks/AuditLog 受益)
- IdeaDetail debate-container 窄屏双栏堆叠(@media 760px 切单列)
- modal-box min-width 改用 min(360px,90vw)(超小窗口不撑破)
- Tasks search-input 改 flex 布局(窄屏自适应宽度)

src/views/ProjectDetail.vue

@@ -821,7 +821,7 @@ onUnmounted(() => {
 }
 
 /* ===== 响应式 ===== */
-@media (max-width: 900px) {
+@media (max-width: 768px) {
   .project-detail { padding: 16px; }
   .detail-grid {
     grid-template-columns: 1fr;