stop existing, possibly in favor of briefcase

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briefcase issues that would need to be resolved to kill Encrust completely:

• overly aggressive restriction on bundle identifiers restricts my idiom beeware/briefcase#1212
• macOS apps aren't portable across x86_64/M1 unless all binary wheels are universal2 beeware/briefcase#1217
• maybe briefcase might hypothetically generate an archive invalid for notarization sometimes when using a zip archive for mac app distribution, and should probably use the recommended command to generate them beeware/briefcase#1218
• Parallelise calls to app signing beeware/briefcase#1201
• codesign --deep is deprecated and should be removed beeware/briefcase#1221

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maybe also need codesigning-without-building-using-briefcase documentation, but I gather this is already at least possible and maybe the docs even exist, need to read up on that before filing anything there