Run oswald-runner, ai and oswl-connector as Flatcar VMs

Replaces the Debian VM that hosted the Gitea Actions runner and adds two
new hosts on goose, all provisioned by Ignition instead of cloud-init:

- oswald-runner: Gitea Actions runner, keeping its registration in
  /var/lib/oswald_runner on disk rather than running ephemeral, which was
  leaving stale offline runners behind whenever a job was interrupted.
- ai: LiteLLM proxy and the Gitea MCP server.
- oswl-connector: tailscaled against headscale, advertising 192.168.7.0/24
  and itself as an exit node.

Their registration tokens and keys come from Infisical through the new
butane_vars plumbing, so nothing secret is committed -- but each one does
land in plaintext in the rendered Ignition snippet on the node, which is
the tradeoff for having no cloud-init here.

The provider gains an ssh block on both nodes because Proxmox has no API
for uploading snippets. That, the snippets content type, and the headscale
preauth key all have to be set up by hand first; flatcar-todo.md has the
steps and the reasoning behind the awkward parts.

Co-Authored-By: Claude Opus 5 <[email protected]>

terraform.tfvars

@@ -195,28 +195,50 @@ nodes = {
         gw           = "192.168.0.1"
       }
     }
-    machines = {
+    # Flatcar Container Linux VMs, provisioned by Ignition. Read
+    # opentofu/README.md (Flatcar section) and flatcar-todo.md before enabling.
+    flatcar = {
       "oswald-runner" = {
-        hostname   = "oswald-runner"
-        vmid       = 202
-        ip         = "192.168.7.50"
-        vlan       = 7
-        template   = "Debian13"
-        full_clone = true
-        onboot     = true
-        tags       = ""
-        agent      = 1
-        memory     = 4096
-        disk_size  = "32"
-        balloon    = 1
-        cpu_type   = "kvm64"
-        cores      = 4
-        sockets    = 1
-        vcpus      = 0
-        bios       = "ovmf"
-        machine    = "q35"
-        bridge     = "vmbr0"
+        hostname         = "oswald-runner"
+        vmid             = 210
+        ip               = "192.168.7.60"
+        vlan             = 7
+        memory           = 4096
+        cores            = 4
+        disk_size        = 32
+        qemu_guest_agent = false
+        # Rendered with templatefile(): ${gitea_runner_token} comes from
+        # Infisical (GITEA_RUNNER_TOKEN in secrets.tmpl), so the token is
+        # never committed.
+        butane_file = "butane/oswald_runner.yaml.tftpl"
       }
+      "ai" = {
+        hostname         = "ai"
+        vmid             = 211
+        ip               = "192.168.7.61"
+        vlan             = 7
+        memory           = 4096
+        cores            = 2
+        disk_size        = 32
+        qemu_guest_agent = false
+        butane_file      = "butane/ai.yaml.tftpl"
+      }
+      # Headscale subnet router / exit node. Registers as an ephemeral node,
+      # so the preauth key must be --ephemeral --reusable; the routes and the
+      # exit node still need approving on the headscale side once it appears.
+      "oswl-connector" = {
+        hostname         = "oswl-connector"
+        vmid             = 212
+        ip               = "192.168.7.62"
+        vlan             = 7
+        memory           = 2048
+        cores            = 2
+        disk_size        = 32
+        qemu_guest_agent = false
+        butane_file      = "butane/oswl_connector.yaml.tftpl"
+      }
+    }
+    machines = {
       "grist" = {
         hostname   = "grist"
         vmid       = 204