fix(HEL-191): 补回问天解势知识文件兜底并消除 Failed to fetch

宿主机 data 挂载会遮盖镜像内 heaven_knowledge.json；增加不受挂载影响的 seed，
并将缺文件/坏 JSON 转为结构化中文错误，前端展示可读提示而非 Failed to fetch。

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: multica-agent <github@multica.ai>

frontend/pages/heaven/page.js

@@ -1363,7 +1363,8 @@ async function interpretHeaven(mode) {
   } catch (error) {
     stopHeavenReadingAnimation();
     state.heavenReadingLoading = false;
-    state.heavenReadingError = error.message || "问天解读失败";
+    const detail = error?.payload?.message || error?.payload?.error || error.message;
+    state.heavenReadingError = detail || "问天解读失败";
     renderHeavenReadingDialog();
     showHeavenNotice(state.heavenReadingError);
     showToast(state.heavenReadingError);