feat(installer): add Windows lba shim (v0.19.64)

[Ivanbeethoven]

Summary

• add a PowerShell installer for libra-windows-amd64.exe with optional SHA-256 verification
• add a managed lba.cmd shim, opt-out switches, and conservative uninstall handling
• publish Windows checksums and document the Windows installation and alias workflow
• cover the PowerShell installer through the Windows compatibility smoke and synchronize release versions to 0.19.64

Impact

Windows users can install the release binary with install.ps1 and invoke Libra through the documented lba shim without overwriting unmanaged binaries or aliases.

Validation

• powershell.exe ... tests/compat/install_alias_windows.ps1
• PowerShell AST parsing for install.ps1 and tests/compat/install_alias_windows.ps1
• cargo +nightly fmt --all -- --check
• git diff --check
• staged diff scope check

cargo test --test compat_install_alias could not run locally because the Windows environment lacks a complete Perl runtime and libclang; the changed installer path is covered directly by the PowerShell smoke.

[Ivanbeethoven]

Superseded by libra-tools#448.