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]>

butane/oswl_connector.yaml.tftpl

@@ -0,0 +1,60 @@
+variant: flatcar
+version: 1.0.0
+
+# Headscale (Tailscale) node: advertises 192.168.7.0/24 as a subnet route and
+# offers itself as an exit node.
+#
+# Registered as an EPHEMERAL node: tailscaled runs with in-memory state, so the
+# VM re-authenticates on every boot and headscale drops the node shortly after
+# it goes offline. That requires the preauth key to be both --ephemeral and
+# --reusable, otherwise the second boot fails to register.
+#
+# HEADSCALE_AUTHKEY is templated in from Infisical (see secrets.tmpl) by
+# main.tf, not stored here. It still ends up in plaintext in the rendered
+# Ignition snippet on the node's storage -- see the caveat in flatcar-todo.md.
+
+systemd:
+  units:
+    - name: tailscaled.service
+      enabled: true
+      contents: |
+        [Unit]
+        Description=Tailscale node (headscale subnet router + exit node)
+        After=docker.service network-online.target
+        Requires=docker.service
+        Wants=network-online.target
+        [Service]
+        TimeoutStartSec=0
+        # tun is not loaded by default on a stock Flatcar boot.
+        ExecStartPre=-/usr/sbin/modprobe tun
+        # Recommended by Tailscale for subnet routers and exit nodes: without
+        # this, UDP throughput through the node is roughly halved.
+        ExecStartPre=-/usr/bin/bash -c 'ethtool -K $(ip route show 0.0.0.0/0 | cut -d" " -f5) rx-udp-gro-forwarding on rx-gro-list off'
+        ExecStartPre=-/usr/bin/docker rm --force tailscaled
+        ExecStart=/usr/bin/docker run --name tailscaled \
+          --network host --cap-add NET_ADMIN --cap-add NET_RAW \
+          --device /dev/net/tun \
+          -e TS_AUTHKEY=${headscale_authkey} \
+          -e TS_HOSTNAME=oswl-connector \
+          -e TS_ROUTES=192.168.7.0/24 \
+          -e TS_ACCEPT_DNS=false \
+          -e "TS_EXTRA_ARGS=--login-server=https://hs.atlashorizon.net --advertise-exit-node" \
+          -e TS_USERSPACE=false \
+          docker.io/tailscale/tailscale:stable
+        ExecStop=/usr/bin/docker stop tailscaled
+        Restart=always
+        RestartSec=5s
+        [Install]
+        WantedBy=multi-user.target
+
+storage:
+  files:
+    # Forwarding must be on for the subnet route and the exit node to pass
+    # traffic at all; the container shares the host netns (--network host), so
+    # this has to be set on the host, not inside it.
+    - path: /etc/sysctl.d/99-tailscale.conf
+      mode: 0644
+      contents:
+        inline: |
+          net.ipv4.ip_forward = 1
+          net.ipv6.conf.all.forwarding = 1