BUG: Path traversal in folder cache sanitization

[andrinoff]

Describe the bug
Folder name sanitization at config/folder_cache.go:67 doesn't prevent ../ sequences. Folder named containing ../ could escape cache directory.

To reproduce

1. Create folder with name like "a/../sensitive"
2. sanitizeFolderName() only replaces / but not ..
3. Cache files written outside intended directory

Expected behavior
Use filepath.Clean() or reject names with ..

Matcha version
master

OS
All

Additional context
File: config/folder_cache.go line 67
Security: path traversal vulnerability