Fix issues with print start

[coffandro]

Purpose of the PR

Fix upload bug and general cleanup

Key Changes Introduced

Removes suffix from NamedTemporaryFile as it blocked valid .gcode files, reason unknown sadly. Non required anyway as SimplyPrint blocks non gcode files on the web side.
Cleans up main.py to respect environment variables rather than hard coding backend and log level.

Testing/Verification Steps

Run program with either testing backend or production backend,
Run program with development enabled,
Run program and try printing gcode file

[timschneider]

Hi @coffandro 👋,

Thank you so much for taking the time to open this pull request—your willingness to improve the project is truly appreciated! 🌟
I noticed that the PR description is currently blank and that several of the changes appear to touch areas not referenced in the title. Would you mind adding a brief summary that covers:

Purpose of the PR
What problem does it solve or feature does it add?

Key Changes Introduced
A short list of the major files or modules affected and why.

Testing/Verification Steps
Any manual steps or automated tests we can run to confirm everything works as intended.

If some changes are unrelated to the main topic, could you let us know whether they belong to this PR (e.g., quick clean-ups) or if you’d prefer to split them into a separate one? This helps keep reviews focused and speeds up the merge process for everyone. 😊

Thanks again for your contribution—looking forward to your update!
Warm regards,
Tim

[coffandro]

I've tried rectifying the issue but I'll wait until I'm back at work and try to retest without the main change of this PR, the suffix

[coffandro]

After retesting I withdraw the suffix bug, it seems to have been caused by a gcode file error, this PR is null.