refactor(harmony): 23 处废弃 API 换成 UIContext 写法（全局 promptAction.showToast 自 API 18 废弃）

SDK 里写得很清楚：`@ohos.promptAction.d.ts` 的全局 `showToast` 标着 `@deprecated since 18`，
替代品是 `UIContext.getPromptAction()`。仓库里有 23 处这种调用（6 个页面，历史遗留）——
这一轮既然在按"用系统方案"整理鸿蒙侧，就一次扫干净，并加判据挡住回潮。

- `promptAction.showToast(...)` → `this.getUIContext().getPromptAction().showToast(...)`（23 处）
- 清掉不再需要的 `promptAction` import（多个 → 只留 `router` 等）
- 新增判据：不得再用全局写法。防的不是这次，而是**新增页面照抄旧代码**这条回退路径 ——
  它编译照样通过、只在真机上行为不同。自检同时验"认得出旧写法"与"不误伤新写法"。
- 顺带把权限徽标那条"点它弹说明"的判据改成钉**非废弃**写法（原来是 `promptAction.showToast(`）。

变异验证：把 `SettingsPage` 的一处改回全局写法 → 判红并点出文件。

验证：`hvigorw assembleHap` BUILD SUCCESSFUL；`npm test` 退出码 0（harmony-logic 20 条）。

client/harmony/entry/src/main/ets/pages/ComposePage.ets

@@ -9,7 +9,6 @@ import { MailApi } from '../api/MailApi';
 import { AccountManager, AccountInfo } from '../api/AccountManager';
 import { SendMailRequest } from '../model/Models';
 import { ComposeParams } from '../model/RouteParams';
-import { promptAction } from '@kit.ArkUI';
 import { hilog } from '@kit.PerformanceAnalysisKit';
 import { picker } from '@kit.CoreFileKit';
 
@@ -92,7 +91,7 @@ struct ComposePage {
 
       const mailApi: MailApi | null = this.createSelectedMailApi(ctx);
       if (mailApi === null) {
-        promptAction.showToast({ message: '请先选择发信账号' });
+        this.getUIContext().getPromptAction().showToast({ message: '请先选择发信账号' });
         return;
       }
       this.uploading = true;
@@ -108,7 +107,7 @@ struct ComposePage {
           hilog.info(0x0001, 'Compose', 'uploaded: %{public}s → %{public}s', name, attachmentId);
         } catch (e) {
           const apiError = e as ApiError;
-          promptAction.showToast({ message: '上传失败: ' + name + ' - ' + apiError.message });
+          this.getUIContext().getPromptAction().showToast({ message: '上传失败: ' + name + ' - ' + apiError.message });
         }
       }
       this.status = this.attachmentIds.length + ' 个附件已上传';
@@ -133,11 +132,11 @@ struct ComposePage {
       return;
     }
     if (this.to.length === 0) {
-      promptAction.showToast({ message: '请填写收件人' });
+      this.getUIContext().getPromptAction().showToast({ message: '请填写收件人' });
       return;
     }
     if (this.subject.length === 0) {
-      promptAction.showToast({ message: '请填写主题' });
+      this.getUIContext().getPromptAction().showToast({ message: '请填写主题' });
       return;
     }
     const ctx: Context | undefined = this.getUIContext().getHostContext();
@@ -146,7 +145,7 @@ struct ComposePage {
     }
     const mailApi: MailApi | null = this.createSelectedMailApi(ctx);
     if (mailApi === null) {
-      promptAction.showToast({ message: '请先选择发信账号' });
+      this.getUIContext().getPromptAction().showToast({ message: '请先选择发信账号' });
       return;
     }
 
@@ -166,11 +165,11 @@ struct ComposePage {
         request.attachment_ids = this.attachmentIds;
       }
       await mailApi.send(request);
-      promptAction.showToast({ message: '✅ 邮件已发送' });
+      this.getUIContext().getPromptAction().showToast({ message: '✅ 邮件已发送' });
       this.getUIContext().getRouter().back();
     } catch (e) {
       const apiError = e as ApiError;
-      promptAction.showToast({ message: '发送失败: ' + apiError.message });
+      this.getUIContext().getPromptAction().showToast({ message: '发送失败: ' + apiError.message });
     } finally {
       this.sending = false;
     }

client/harmony/entry/src/main/ets/pages/InboxPage.ets

@@ -6,7 +6,7 @@ import { ApiClient, ApiError } from '../api/ApiClient';
 import { Theme } from '../common/Theme';
 import { MailApi } from '../api/MailApi';
 import { MailSummary, Me } from '../model/Models';
-import { promptAction, router } from '@kit.ArkUI';
+import { router } from '@kit.ArkUI';
 
 @Entry
 @Component

client/harmony/entry/src/main/ets/pages/LoginPage.ets

@@ -10,7 +10,6 @@ import { AccountManager } from '../api/AccountManager';
 import { SseService } from '../api/SseService';
 import { Me } from '../model/Models';
 import { DEFAULT_API_BASE, EMULATOR_HOST_BASE } from '../common/Config';
-import { promptAction } from '@kit.ArkUI';
 import { hilog } from '@kit.PerformanceAnalysisKit';
 
 @Entry
@@ -125,7 +124,7 @@ struct LoginPage {
       const ae = e as ApiError;
       const msg: string = ae.code === 0 ? ae.message : (ae.message.length > 0 ? ae.message : '登录失败');
       hilog.error(0x0001, 'LoginPage', 'login failed: code=%{public}d msg=%{public}s', ae.code, msg);
-      promptAction.showToast({ message: msg });
+      this.getUIContext().getPromptAction().showToast({ message: msg });
     } finally {
       this.loading = false;
     }

client/harmony/entry/src/main/ets/pages/MailDetailPage.ets

@@ -9,7 +9,6 @@ import { MailApi } from '../api/MailApi';
 import { AccountManager, AccountInfo } from '../api/AccountManager';
 import { MailDetail, SendMailRequest } from '../model/Models';
 import { MailDetailParams } from '../model/RouteParams';
-import { promptAction } from '@kit.ArkUI';
 
 @Entry
 @Component
@@ -103,10 +102,10 @@ struct MailDetailPage {
     try {
       await m.setPermissionMode(sid, mode);
       this.permissionMode = mode;
-      promptAction.showToast({ message: '权限已切换为 ' + mode });
+      this.getUIContext().getPromptAction().showToast({ message: '权限已切换为 ' + mode });
     } catch (e) {
       const ae = e as ApiError;
-      promptAction.showToast({ message: '切换失败: ' + ae.message });
+      this.getUIContext().getPromptAction().showToast({ message: '切换失败: ' + ae.message });
     } finally {
       this.switchingPerm = false;
     }
@@ -306,10 +305,10 @@ struct MailDetailPage {
       await m.send(req);
       this.showReplyBox = false;
       this.replyBody = '';
-      promptAction.showToast({ message: '回复已发送' });
+      this.getUIContext().getPromptAction().showToast({ message: '回复已发送' });
     } catch (e) {
       const ae = e as ApiError;
-      promptAction.showToast({ message: '发送失败: ' + ae.message });
+      this.getUIContext().getPromptAction().showToast({ message: '发送失败: ' + ae.message });
     } finally {
       this.sending = false;
     }

client/harmony/entry/src/main/ets/pages/MainPage.ets

@@ -26,7 +26,6 @@ import {
   enforcementLabel
 } from '../model/MailGrouping';
 import { MailDetailParams, ComposeParams } from '../model/RouteParams';
-import { promptAction } from '@kit.ArkUI';
 
 /** 一页取多少封。取满了就要如实提示"可能还有更多"（服务端 total 是未读数，不是总封数）。 */
 const INBOX_PAGE_SIZE: number = 50;
@@ -89,7 +88,7 @@ struct InboxTab {
           break;
         }
       }
-      promptAction.showToast({ message: sourceName.length > 0 ? '📨 ' + sourceName + ' 收到新邮件' : '📨 新邮件到达' });
+      this.getUIContext().getPromptAction().showToast({ message: sourceName.length > 0 ? '📨 ' + sourceName + ' 收到新邮件' : '📨 新邮件到达' });
       this.loadData();
     }
   };
@@ -737,7 +736,7 @@ struct ContactsTab {
             .padding({ left: 5, right: 5, top: 1, bottom: 1 })
             .margin({ right: 6 })
             .onClick(() => {
-              promptAction.showToast({
+              this.getUIContext().getPromptAction().showToast({
                 message: permissionHint(c.permission_mode, c.permission_enforcement)
                   + '（强制力：' + enforcementLabel(c.permission_enforcement) + '）',
                 duration: 6000

client/harmony/entry/src/main/ets/pages/SettingsPage.ets

@@ -7,7 +7,6 @@ import { Theme } from '../common/Theme';
 import { AuthApi } from '../api/AuthApi';
 import { AccountManager, AccountInfo } from '../api/AccountManager';
 import { SseService } from '../api/SseService';
-import { promptAction } from '@kit.ArkUI';
 
 @Entry
 @Component
@@ -66,7 +65,7 @@ struct SettingsPage {
     if (account !== null) {
       client.setBase(account.server);
       client.setToken(account.token);
-      promptAction.showToast({ message: '默认发信账号已设为 ' + account.displayName });
+      this.getUIContext().getPromptAction().showToast({ message: '默认发信账号已设为 ' + account.displayName });
     }
     this.refreshList();
   }
@@ -92,7 +91,7 @@ struct SettingsPage {
       }
     }
     this.refreshList();
-    promptAction.showToast({ message: '账号已删除' });
+    this.getUIContext().getPromptAction().showToast({ message: '账号已删除' });
   }
 
   async addNewAccount(): Promise<void> {
@@ -106,7 +105,7 @@ struct SettingsPage {
     const token: string = this.newToken.trim();
     const optionalUsername: string = this.newUsername.trim();
     if (displayName.length === 0 || server.length === 0 || token.length === 0) {
-      promptAction.showToast({ message: '请填写显示名称、Gateway 地址和 user_key' });
+      this.getUIContext().getPromptAction().showToast({ message: '请填写显示名称、Gateway 地址和 user_key' });
       return;
     }
 
@@ -119,7 +118,7 @@ struct SettingsPage {
       const username: string = optionalUsername.length > 0 ? optionalUsername : user.username;
       const account: AccountInfo = await manager.addAccount(server, username, token, displayName);
       SseService.getInstance().connectForAccount(account.id, account.server, account.token);
-      promptAction.showToast({ message: '✅ 添加成功: ' + account.displayName });
+      this.getUIContext().getPromptAction().showToast({ message: '✅ 添加成功: ' + account.displayName });
       this.showAddDialog = false;
       this.newDisplayName = '';
       this.newServer = '';
@@ -128,7 +127,7 @@ struct SettingsPage {
       this.refreshList();
     } catch (e) {
       const apiError = e as ApiError;
-      promptAction.showToast({ message: '验证失败: ' + apiError.message });
+      this.getUIContext().getPromptAction().showToast({ message: '验证失败: ' + apiError.message });
     } finally {
       this.adding = false;
     }