fix(release): build host Linux binaries with glibc floor

[pimlock]

Summary

Build host-executed Linux gateway and VM driver artifacts with an explicit glibc 2.31 floor, and fail installer package installs early on unsupported libc environments.

Related Issue

Closes #1456

Changes

• Build openshell-gateway and openshell-driver-vm Linux artifacts with cargo zigbuild targets pinned to glibc 2.31.
• Verify uploaded host ELF binaries do not reference GLIBC_* symbols newer than 2.31.
• Make Debian, RPM, and gateway image staging consume the same portable host gateway binary.
• Add install.sh glibc detection and preflight errors before package downloads.
• Add release artifact smoke tests for Ubuntu 20.04, Ubuntu 22.04, and Rocky Linux 9 on amd64 and arm64.
• Document Linux artifact compatibility and the package glibc requirement.

Testing

• mise run test:install-sh
• sh -n install.sh
• bash -n tasks/scripts/verify-glibc-symbols.sh tasks/scripts/test-install-sh.sh tasks/scripts/stage-prebuilt-binaries.sh
• Modified GitHub workflow YAML parsed with Ruby YAML parser
• git diff --check
• mise run docs
• mise run pre-commit passes

mise run pre-commit ran Rust tests successfully but failed license:check because unrelated untracked test-policy.yaml in the local worktree is missing an SPDX header. That file is not part of this PR.

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)

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