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/Dashboard.vue

@@ -140,8 +140,8 @@ onMounted(() => {
 
 /* ═══ Responsive ═══ */
 
-/* 窄窗口：单栏 */
-@media (max-width: 900px) {
+/* 窄窗口：单栏(与 AppLayout 768px 断点对齐) */
+@media (max-width: 768px) {
   .dashboard { padding: 12px 14px 16px; }
   .dash-grid { grid-template-columns: 1fr; }
   .dash-right { flex-direction: row; flex-wrap: wrap; gap: 10px; }