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>

runners/Pulumi.yaml

@@ -0,0 +1,12 @@
+name: foundation-runners
+description: >-
+  Step-0-after-foundation — the fenced Forgejo Actions runner fleet on libvirt
+  hosts (e.g. crunchy01), as an ISOLATED stack. Decoupled from `bootstrap` on
+  purpose: a @pulumi/libvirt provider dials the runner host on every up/refresh,
+  so keeping it here (never imported by bootstrap) means foundation ops never
+  require — and are never blocked by — the runner host. One-way dependency: needs
+  the forge up to mint a runner token (i.e. runs after the foundation stands).
+runtime:
+  name: nodejs
+  options:
+    packagemanager: bun