Curse forge install and startup fixes

[aadiaz1804]

Description

Fix CurseForge Generic egg startup command and API key handling.

• Remove quotes from printf %s argfile paths in startup command so Java parses @user_jvm_args.txt and @unix_args.txt correctly instead of treating them as class names
• Conditionally include -Xmx flag only when SERVER_MEMORY > 0, preventing invalid -Xmx0M when memory is set to unlimited
• Fix CurseForge API key $ signs being mangled by using single quotes on the static header portion (already committed to branch)

Resolves startup errors:

• Could not find or load main class "@user_jvm_args.txt"
• Invalid maximum heap size: -Xmx0M

Checklist for all submissions

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you tested and reviewed your changes with confidence that everything works?
• Did you branch your changes and PR from that branch and not from your master branch?
  • If not, why?:

• You verify that the start command applied does not use a shell script
  • If some script is needed then it is part of a current yolk or a PR to add one
• The egg was exported from the panel

[Superpaul209]

I have installed the egg json from this pull request on a fresh instance, it works perfectly thanks.