feat(release): add Webi installation contract

[realmroot]

Summary

• document official Webi installation for stable and explicit Realmroot versions
• document the production merge/deployment boundary
• add a focused release-asset verifier for the GoReleaser archive/checksum contract
• keep normal PR CI and the tag release workflow unchanged

Closes #10.

Official installer contribution

The official installer contribution is open at:

• feat(realmroot): add installer webinstall/webi-installers#1126
• source: saltbo/webi-installers:feat/realmroot-installer

The upstream PR requests a maintainer-controlled Beta deployment and these smoke tests:

curl -sS https://beta.webi.sh/realmroot@stable | sh
realmroot version
curl -sS https://beta.webi.sh/realmroot@0.4.2 | sh
realmroot version

Production https://webi.sh/realmroot and https://webi.ms/realmroot become usable only after upstream merge and deployment. There is intentionally no Realmroot-hosted Webi origin or temporary endpoint.

Verification

• make verify
• go vet ./...
• goreleaser check
• release verifier validated all six GoReleaser archives and their published checksums
• corrupted snapshot archive failed checksum verification
• upstream go test ./...: 147 tests passed across 45 packages
• upstream cache refresh classified 30 Realmroot release assets, including all six v0.4.2 OS/architecture targets
• Prettier, shfmt, ShellCheck, and PowerShell parser checks passed
• generated macOS/arm64 installer installed v0.4.2; corrupted cached archive failed closed and was removed

Normal CLI PR CI remains the existing go test, go vet, go build, and goreleaser check job. The six-target CI performance optimization is deferred.

---

_{🤖 Created by Jarvis via Realmroot}