fix(host): make libvirt stack enablement mutually exclusive so one stack cannot silently kill the other's sockets (#3126)

[Xore]

Monolithic libvirtd and modular virt*d stacks both bind
/run/libvirt/libvirt-sock(-ro) with Conflicts= between their units. When
both stacks are enabled at once, starting one instantly closes the
other's sockets — socket units carry no Restart=, so recovery needs
manual re-enablement. Reproduced live on the host installer.

step_libvirt_install now disables the opposite stack's units before
enabling its own: the monolithic arm disables virtproxyd.socket/-ro
before enabling libvirtd; the modular arm disables libvirtd.* before
enabling the virt*d sockets.

Times in this description: Europe/Berlin.

Closes #3126

[strix-security]

Strix Security Review

No security issues found.

_{Updated for 1b29951.}

---

Reviewed by Strix
_{Re-run review · Configure security review settings}

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[strix-security]

Reviewed the single changed file, scripts/install-homeserver.sh. The change adjusts step_libvirt_install() to disable the opposite libvirt stack's systemd units before enabling its own, preventing the Conflicts= socket-kill hazard described in #3126. All systemctl arguments are hardcoded unit-name literals with no user-controlled input or dynamic expansion, so no injection or other security issue is introduced. No findings.

---

Reviewed by Strix
_{Configure security review settings}