Add Gatekeeper app

[enexis1337]

Application Submission

• Gatekeeper is a password manager for Flipper Zero that uses BadUSB (HID emulation) to automatically type stored credentials into a computer.

Features:

• Stores up to 30 credentials
• Master Combo protection (4 directional inputs required on launch)
• Custom labels and icons for entries
• Instant password injection via BadUSB

Extra Requirements

• No extra hardware required. Works on any Flipper Zero with BadUSB support.

Author Checklist (Fill this out)

• I've read the contribution guidelines and my PR follows them
• I own the code I'm submitting or have code owner's permission to submit it
• I have validated the manifest file(s) with python3 tools/bundle.py --nolint applications/CATEGORY/APPID/manifest.yml bundle.zip

Reviewer Checklist (Don't fill this out)

• Bundle is valid
• There are no obvious issues with the source code
• I've ran this application and verified its functionality

[xMasterX]

Hello, app works ok, but there's an issue with manifest and screenshots

1 - list and setcombo pics should be 512x256 in size
2 - manifest is missing .png at iconsselect picture

Please fix that and update commit sha in manifest after pushing pics with correct size in your repo, don't forget to add .png to last one

[enexis1337]

Hello, app works ok, but there's an issue with manifest and screenshots

1 - list and setcombo pics should be 512x256 in size 2 - manifest is missing .png at iconsselect picture

Please fix that and update commit sha in manifest after pushing pics with correct size in your repo, don't forget to add .png to last one

Done! Everything fixed according to your comments. Thanks.