feat(runners): decoupled Pulumi stack for the fenced runner fleet (R5)

A separate, isolated Pulumi project (peer to bootstrap/provision/offsite-backup)
that provisions runner VM(s) on a libvirt host and registers Forgejo Actions
runners with a distinct `fenced` label — so ecosystem/untrusted jobs run OFF the
forge VM.

Decoupled ON PURPOSE: a @pulumi/libvirt provider dials the runner host on every
up/refresh, so keeping it in `bootstrap` would make the foundation undeployable/
unrefreshable whenever the host (crunchy01) is down or unreachable (the Terraform
coupling trap). As its own stack, bootstrap never imports it — foundation ops
never touch crunchy01, and this stack's health is independent. One-way dependency:
it mints a runner token FROM the forge, i.e. runs after the foundation stands.

Codifies what was built + hardened by hand this session (runners/README.md):
Ubuntu VM on the LAN bridge (docker + qemu-guest-agent via cloud-init), the
kube-router-proof FORWARD timer, and runner registration. Typechecked; the live
`pulumi up` cutover from the hand-built VM is the remaining validation step.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -11,3 +11,4 @@ provision/state/
 offsite-backup/state/
 offsite-backup/Pulumi.prod.yaml
 provision/Pulumi.foundation-test.yaml
+runners/state/