fix: improve installation error handling with actionable suggestions (#343)

- Add error classification helpers for permission, file-not-found, and filesystem errors
- Handle empty/corrupt config files gracefully with recovery suggestions
- Add 60-second timeout to runBunInstall() to prevent hanging forever
- Improve error messages with specific recovery suggestions for each error type
- Export BunInstallResult type with detailed error info (success, timedOut, error)
- Handle SyntaxError in JSON parsing with user-friendly suggestions
- Add validation for config file contents (empty, whitespace-only, non-object)

Fixes #338

Co-authored-by: sisyphus-dev-ai <[email protected]>

Author: sisyphus-dev-ai