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/styles/global.css

@@ -193,7 +193,7 @@ html, body, #app {
   border: 0.5px solid var(--df-border);
   border-radius: var(--df-radius-lg);
   padding: 24px;
-  min-width: 360px;
+  min-width: min(360px, 90vw);
   max-width: 90vw;
 }
 .modal-title { font-size: 18px; font-weight: 500; color: var(--df-text); margin-bottom: 16px; }
@@ -227,7 +227,7 @@ html, body, #app {
 .back-link:hover { text-decoration: underline; }
 
 /* — Filter Bar(列表页筛选 + 搜索)— Ideas / Tasks 共享 */
-.filter-bar { display: flex; gap: 8px; margin-bottom: var(--df-gap-page); align-items: center; }
+.filter-bar { display: flex; gap: 8px; margin-bottom: var(--df-gap-page); align-items: center; flex-wrap: wrap; }
 .filter-btn {
   padding: 6px 14px;
   border: 0.5px solid var(--df-border);