Feature request: 'Secure Folder' support

### Please check before submitting an issue

- [x] I am using the latest version of App Manager
- [x] I have searched the issues and haven't found anything relevant
- [x] I have read the docs
- [x] I know that generating a report, in whole part or in part, using AI/LLM is prohibited

### Describe the new feature

Rikka AppOps does it with Shizuku but App Manager has features AppOps lacks - it's a workhorse. I see there's support for work/Island profiles. Would be awesome to see Secure Folder support. Rikka AppOps is able to do this with a single installation on the main device profile.

Either way, @MuntashirAkon I love you. You are a role model and a true philanthropist!

App Manager is a crown jewel of the Android open source ecosystem. So feature rich and robust not to mention intuitive which is saying something for something so rich with information and options.

### Describe the solution you'd like

NA

### Describe alternatives you've considered

NA

### Additional context

NA

Start by reviewing App Manager's existing support for work and Island profiles, then compare the single-installation Secure Folder behavior described for Rikka AppOps. Done would mean defining and implementing Secure Folder support, but the issue provides no files, tests, or concrete solution details.

Written by the indexing model from the issue text.