refactor(speaking): generateGreeting catch 从 any 收紧到 unknown

- catch (err: unknown):符合 TS 4.0+ 推荐,与计划里 Task 6 startDialogue 一致
- AbortError 检测改为 err instanceof Error && err.name === 'AbortError'
- err.message 经 instanceof Error 守卫再传给 friendlyErrorMessage

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/views/Editor/EnglishSpeaking/composables/useDialogueEngine.ts

@@ -50,10 +50,10 @@ export function useDialogueEngine(mode: 'preview' | 'real' = 'preview') {
       aiMsg.content = aiMessage
       aiMsg.status = 'done'
       speakTTS(aiMessage)
-    } catch (err: any) {
-      if (err?.name === 'AbortError') return  // 组件卸载:不改 UI
+    } catch (err: unknown) {
+      if (err instanceof Error && err.name === 'AbortError') return  // 组件卸载:不改 UI
       aiMsg.status = 'error'
-      aiMsg.error = friendlyErrorMessage(err?.message)
+      aiMsg.error = friendlyErrorMessage(err instanceof Error ? err.message : undefined)
       const status = err instanceof DialogueApiError ? err.status : undefined
       aiMsg.unrecoverable = status === 404 || status === 409
     } finally {