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/i18n/locales/en.json

@@ -675,6 +675,34 @@
     "installFailed": "Failed to install",
     "uninstallSuccess": "Skill {{name}} uninstalled",
     "uninstallFailed": "Failed to uninstall",
+    "error": {
+      "skillNotFound": "Skill not found: {{directory}}",
+      "missingRepoInfo": "Missing repository info (owner or name)",
+      "downloadTimeout": "Download repository {{owner}}/{{name}} timeout ({{timeout}}s)",
+      "downloadTimeoutHint": "Please check network connection or retry later",
+      "skillPathNotFound": "Skill path '{{path}}' not found in repository {{owner}}/{{name}}",
+      "skillDirNotFound": "Skill directory not found: {{path}}",
+      "emptyArchive": "Downloaded archive is empty",
+      "downloadFailed": "Download failed: HTTP {{status}}",
+      "allBranchesFailed": "All branches failed, tried: {{branches}}",
+      "httpError": "HTTP error {{status}}",
+      "http403": "GitHub access restricted, possibly rate limited",
+      "http404": "Repository or branch not found, please check URL",
+      "http429": "Too many requests, please wait and retry",
+      "parseMetadataFailed": "Failed to parse skill metadata",
+      "getHomeDirFailed": "Unable to get user home directory",
+      "networkError": "Network error",
+      "fsError": "File system error",
+      "unknownError": "Unknown error",
+      "suggestion": {
+        "checkNetwork": "Please check network connection",
+        "checkProxy": "Consider configuring HTTP proxy",
+        "retryLater": "Please retry later",
+        "checkRepoUrl": "Please check repository URL and branch name",
+        "checkDiskSpace": "Please check disk space",
+        "checkPermission": "Please check directory permissions"
+      }
+    },
     "repo": {
       "title": "Manage Skill Repositories",
       "description": "Add or remove GitHub skill repository sources",