Added unversioned TeamID infrastructure.

[JanX2]

This is described in detail in the file "Shared.xcconfig".

[schappim]

Thanks for the thoughtful contribution, @JanX2! 🙏 The unversioned TeamID pattern is genuinely good practice for multi-contributor projects, and your Shared.xcconfig is well-documented. Closing this one though, because:

• macOCR is effectively solo-maintained, so the main benefit (letting multiple contributors sign locally without stomping on each other's TeamID in project.pbxproj) doesn't really apply here.
• It adds setup friction — anyone cloning the repo (including me, coming back to it after a while) would need to create DEVELOPMENT_TEAM.xcconfig before the project builds, which is extra ceremony for a tool I don't open Xcode for often.
• The PR also hardcodes a TeamID (FK9S39L3SK) in the committed DEVELOPMENT_TEAM.xcconfig, which would need to be stripped before merge.

If the project ever grows multiple signing contributors I'll revisit this approach — really appreciate you documenting it so clearly.