Publish portable ZIP releases

[rimtty]

Summary

• make the self-contained Windows x64 ZIP the official public distribution artifact
• stop uploading unsigned MSI artifacts while retaining MSI build coverage for future signed distribution
• add checksum, SmartScreen, portable install, update, and removal guidance
• prepare version 0.1.1 as the first downloadable binary release

Why

A publicly trusted code-signing option is not currently available at a sustainable cost. Publishing an unsigned MSI would conflict with the release policy, while the existing self-contained portable ZIP provides a practical and clearly disclosed distribution path.

Validation

• dependency vulnerability audit: 0 vulnerable package entries
• repository public-readiness scan: passed
• formatting: passed
• Release build: passed with 0 warnings and 0 errors
• portable v0.1.1 package: generated and checksum verified
• automated tests: 431/432 passed locally; one existing native USER-handle test is environment-sensitive and remains for clean GitHub CI validation