fix(ui): 统一 payment 和 settlement 模块浮动底栏为 fixed 定位

- payment 模块所有表单页底栏按钮顺序及布局全量对齐，取消居中改为右对齐浮动
- settlement 模块弹窗及独立页 footer 添加 sticky 浮动，主操作按钮样式调整为 plain
- 彻底修复浮动底栏不吸底问题，所有相关 footer 由 position: sticky 改为 position: fixed
- 统一 fixed 底栏样式模板，包含左偏移支持侧栏折叠和横向布局切换
- 更新项目文档，明确浮动底栏必须用 fixed 定位，避免 overflow:hidden 祖先导致 sticky 失效
- 清理所有残留 sticky 样式，确保底栏始终固定在视口底部，提升用户体验

src/views/settlement/components/formal-settlement-editor.vue

@@ -1549,12 +1549,21 @@ export default {
   padding: 12px 24px;
   border-top: 1px solid #eff1f7;
   gap: 12px;
-  position: sticky;
+  position: fixed;
+  right: 0;
+  left: 230px;
   bottom: 0;
   z-index: 10;
+  margin: 0;
   background: #fff;
   box-shadow: 0 -2px 8px rgba(0, 0, 0, 0.06);
 }
+:global(.avue--collapse) .formal-editor__page-actions {
+  left: 60px;
+}
+:global(.avue-layout--horizontal) .formal-editor__page-actions {
+  left: 0;
+}
 .formal-editor__links {
   display: flex;
   flex-wrap: wrap;

src/views/settlement/components/pre-settlement-editor.vue

@@ -1532,8 +1532,11 @@ export default {
     padding: 12px 24px;
     border-top: 1px solid #eff1f7;
     gap: 12px;
-    position: sticky;
+    position: fixed;
+    right: 0;
+    left: 230px;
     bottom: 0;
+    margin: 0;
     z-index: 10;
     background: #fff;
     box-shadow: 0 -2px 8px rgba(0, 0, 0, 0.06);
@@ -1651,4 +1654,10 @@ export default {
 :deep(.pre-settlement-candidate-dialog .el-table__body tr:nth-child(even) > td.el-table__cell) {
   background: #fafafa;
 }
+:global(.avue--collapse .pre-settlement-editor__page-actions) {
+  left: 60px;
+}
+:global(.avue-layout--horizontal .pre-settlement-editor__page-actions) {
+  left: 0;
+}
 </style>