feat(cli): add MSI install scope and default it to per-user

[nikuda]

MSI installers from dx bundle now default to per-user: %LOCALAPPDATA%\Programs\<product>, InstallScope="perUser", InstallPrivileges="limited", no UAC. That matches the existing NSIS default (CurrentUser). Per-machine (ProgramFiles, elevated) is opt-in.

Previously the WiX template hardcoded InstallScope="perMachine" with no config.

Config

[bundle.windows.wix]
install_scope = "PerUser"    # default if omitted
# install_scope = "PerMachine"

Breaking changes

Stock dx bundle --package-types msi (no install_scope) installs per-user instead of per-machine.

Test plan

• Parse: omitted [bundle.windows.wix] → PerUser; install_scope = "PerMachine" → PerMachine
• Template: per-user uses LocalAppDataFolder\Programs and InstallPrivileges="limited"; per-machine keeps ProgramFiles*Folder

[nikuda]

This one need a bit more wiring, the core is right but I don't think the changes propagate all the way out to user config.