style(project-apply): 统一弹窗和独立表单底栏按钮风格

- 统一「保存+提交+返回」按钮的视觉层级和排序
- 按次要（默认）、中间（primary plain）、主操作（primary）三档区分按钮样式
- 调整按钮顺序为「辅助→返回/取消→保存草稿→提交」，主操作始终最右
- 修改project-apply、invoice-receipt-form、invoice-application-form三个页面的按钮实现
- 在 MEMORY.md 中新增底栏按钮统一规则说明
- 保留已合规页面按钮风格，避免重复修改

src/views/business/project-apply.vue

@@ -619,20 +619,22 @@
         :class="{ 'project-apply-dialog__footer--change': isChangeDialog }"
       >
           <template v-if="isChangeDialog">
-            <el-button type="primary" :loading="submitLoading" @click="saveChangeProject">
+            <el-button v-if="!isProjectFormPage" @click="handleCancelProject">取消</el-button>
+            <el-button v-if="isProjectFormPage" @click="closeProjectForm">返回</el-button>
+            <el-button type="primary" plain :loading="submitLoading" @click="saveChangeProject">
               保存
             </el-button>
             <el-button type="primary" :loading="submitLoading" @click="submitChangeProject">
               提交
             </el-button>
-            <el-button v-if="!isProjectFormPage" @click="handleCancelProject">取消</el-button>
-            <el-button v-if="isProjectFormPage" @click="closeProjectForm">返回</el-button>
           </template>
           <template v-else>
             <el-button v-if="!isProjectFormPage" @click="handleCancelProject">取消</el-button>
+            <el-button v-if="isProjectFormPage" @click="closeProjectForm">返回</el-button>
             <el-button
               v-if="!dialogReadonly"
               type="primary"
+              plain
               :loading="submitLoading"
               @click="saveProject"
             >
@@ -646,7 +648,6 @@
             >
               提交
             </el-button>
-            <el-button v-if="isProjectFormPage" @click="closeProjectForm">返回</el-button>
           </template>
       </div>
     </component>