feat(skills): enhance error messages with i18n support

- Add structured error format with error codes and context
- Create skillErrorParser to format errors for user-friendly display
- Add comprehensive i18n keys for all skill-related errors (zh/en)
- Extend download timeout from 15s to 60s to reduce false positives
- Fix: Pass correct error title based on operation context (load/install/uninstall)

Error improvements:
- SKILL_NOT_FOUND: Show skill directory name
- DOWNLOAD_TIMEOUT: Display repo info and timeout duration with network suggestion
- DOWNLOAD_FAILED: Show HTTP status code with specific suggestions (403/404/429)
- SKILL_DIR_NOT_FOUND: Show full path with URL check suggestion
- EMPTY_ARCHIVE: Suggest checking repository URL

Users will now see detailed error messages instead of generic "Error".

src/lib/errors/skillErrorParser.ts

@@ -0,0 +1,104 @@
+import { TFunction } from "i18next";
+
+/**
+ * 结构化错误对象
+ */
+export interface SkillError {
+  code: string;
+  context: Record<string, string>;
+  suggestion?: string;
+}
+
+/**
+ * 尝试解析后端返回的错误字符串
+ * 如果是 JSON 格式，返回结构化错误；否则返回 null
+ */
+export function parseSkillError(errorString: string): SkillError | null {
+  try {
+    const parsed = JSON.parse(errorString);
+    if (parsed.code && parsed.context) {
+      return parsed as SkillError;
+    }
+  } catch {
+    // 不是 JSON 格式，返回 null
+  }
+  return null;
+}
+
+/**
+ * 将错误码映射到 i18n key
+ */
+function getErrorI18nKey(code: string): string {
+  const mapping: Record<string, string> = {
+    SKILL_NOT_FOUND: "skills.error.skillNotFound",
+    MISSING_REPO_INFO: "skills.error.missingRepoInfo",
+    DOWNLOAD_TIMEOUT: "skills.error.downloadTimeout",
+    DOWNLOAD_FAILED: "skills.error.downloadFailed",
+    SKILL_DIR_NOT_FOUND: "skills.error.skillDirNotFound",
+    EMPTY_ARCHIVE: "skills.error.emptyArchive",
+    GET_HOME_DIR_FAILED: "skills.error.getHomeDirFailed",
+  };
+
+  return mapping[code] || "skills.error.unknownError";
+}
+
+/**
+ * 将建议码映射到 i18n key
+ */
+function getSuggestionI18nKey(suggestion: string): string {
+  const mapping: Record<string, string> = {
+    checkNetwork: "skills.error.suggestion.checkNetwork",
+    checkProxy: "skills.error.suggestion.checkProxy",
+    retryLater: "skills.error.suggestion.retryLater",
+    checkRepoUrl: "skills.error.suggestion.checkRepoUrl",
+    checkPermission: "skills.error.suggestion.checkPermission",
+    http403: "skills.error.http403",
+    http404: "skills.error.http404",
+    http429: "skills.error.http429",
+  };
+
+  return mapping[suggestion] || suggestion;
+}
+
+/**
+ * 格式化技能错误为用户友好的消息
+ * @param errorString 后端返回的错误字符串
+ * @param t i18next 翻译函数
+ * @param defaultTitle 默认标题的 i18n key（如 "skills.installFailed"）
+ * @returns 包含标题和描述的对象
+ */
+export function formatSkillError(
+  errorString: string,
+  t: TFunction,
+  defaultTitle: string = "skills.installFailed"
+): { title: string; description: string } {
+  const parsedError = parseSkillError(errorString);
+
+  if (!parsedError) {
+    // 如果不是结构化错误，返回原始错误字符串
+    return {
+      title: t(defaultTitle),
+      description: errorString || t("common.error"),
+    };
+  }
+
+  const { code, context, suggestion } = parsedError;
+
+  // 获取错误消息的 i18n key
+  const errorKey = getErrorI18nKey(code);
+
+  // 构建描述（错误消息 + 建议）
+  let description = t(errorKey, context);
+
+  // 如果有建议，追加到描述中
+  if (suggestion) {
+    const suggestionKey = getSuggestionI18nKey(suggestion);
+    const suggestionText = t(suggestionKey);
+    description += `\n\n${suggestionText}`;
+  }
+
+  return {
+    title: t(defaultTitle),
+    description,
+  };
+}