fix(snipped): properly parse and set output file for saved screenshots

[Marshall-Hallenbeck]

Description

After #1121, I looked at our other uses of saving files automatically and how we constructed paths for the output files and found one location that was somewhat vulnerable. The snipped module does not parse served pathnames correctly, so you can write to arbitrary folders via absolute paths, but you can't control what the filename is mostly, so this is more so a bugfix than anything (the module was redundantly adding the path to the saved filename as well, so I fixed that).

I used AI to help create a POC, but the code in this PR itself was written by me.

Type of change

Insert an "x" inside the brackets for relevant items (do not delete options)

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Deprecation of feature or functionality
• This change requires a documentation update
• This requires a third party update (such as Impacket, Dploot, lsassy, etc)
• This PR was created with the assistance of AI (list what type of assistance, tool(s)/model(s) in the description)

Setup guide for the review

Requires files in the $User/Screenshots/ directory

Screenshots (if appropriate):

Before:

After:

Checklist:

Insert an "x" inside the brackets for completed and relevant items (do not delete options)

• I have ran Ruff against my changes (poetry: poetry run ruff check ., use --fix to automatically fix what it can)
• I have added or updated the tests/e2e_commands.txt file if necessary (new modules or features are required to be added to the e2e tests)
• If reliant on changes of third party dependencies, such as Impacket, dploot, lsassy, etc, I have linked the relevant PRs in those projects
• I have linked relevant sources that describes the added technique (blog posts, documentation, etc)
• I have performed a self-review of my own code (not an AI review)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (PR here: https://github.com/Pennyw0rth/NetExec-Wiki)

[NeffIsBack]

LGTM