Add portable unsigned Beta 9.1 test build

[WebCrew]

Summary

• publish a portable ZIP beside the diagnostic NSIS installer for unsigned preview releases
• avoid Windows installation and uninstall registration during routine functional testing
• checksum both artifacts and verify the packaged executable exists before publication
• document that the portable executable remains unsigned and must not be used to bypass Smart App Control
• publish the correction as 0.5.0-beta.9.1

Reason

Smart App Control blocked the unsigned NSIS Un_H.exe helper while uninstalling Beta 8, despite earlier preview uninstallers having completed. The portable archive removes NSIS uninstall behavior from the routine maintainer test path while trusted SignPath signing remains pending.

Verification

• node scripts/check.cjs
• GitHub Windows workflow must build the NSIS package, create the portable ZIP, and checksum both