feat(vpn-ingress): WireGuard remote access on udp/51820 (hostNetwork, declarative peers)

Lets the operator's Android / Linux / Windows / macOS devices dial in from
anywhere and behave like LAN machines: full reach to 192.168.2.0/24 plus
internet egress out the house WAN. Opposite direction to platform/vpn-egress,
which sends pods OUT through PIA; the two share nothing but the word "VPN".

WireGuard because it is the only option with a first-party client on all four
named platforms, and because its handshake MAC is keyed with the responder's
own public key: an unauthenticated packet gets NO reply, so udp/51820 is
indistinguishable from a closed port. That, not "it is encrypted", is what
makes an unfiltered WAN port defensible, and why there is no source allowlist.

hostNetwork: true is REQUIRED, not convenient. A pod-networked server must SNAT
clients to its own pod IP, so every remote client would carry that pod's Cilium
identity -- and a pod-sourced request to the shared Gateway VIP returns 403 from
Envoy for ALL 16 hostnames (measured 2026-10-04), because Cilium's Gateway
preserves the original source identity and enforces the destination's ingress
policy. The obvious build would have shipped a healthy-looking tunnel on which
every cluster web UI was 403 and *.home.keithjackson.dev did not even resolve.
In the host netns traffic is SNATed to the node and arrives as host/remote-node,
exactly like a LAN client. It also sidesteps the unsafe ip_forward sysctl, the
L2-announcement lease lottery, and double encapsulation (hence MTU 1420).
Permitted by restrict-host-namespaces' own carve-out for platform namespaces.
The cost is stated in networkpolicy.yaml rather than papered over: no
NetworkPolicy constrains a hostNetwork pod.

A DaemonSet so the hand-made WAN forward cannot be invalidated by a reschedule;
all three nodes answer the same keys, so failover is a one-line router change.

Peer PUBLIC keys are plaintext in peers.yaml, which makes "who can get into my
house" a reviewable PR diff. The only secret -- the server's private key -- is
an out-of-band Secret: an agent must not mint a long-lived private key, and the
two halves are joined only at pod start into a tmpfs that dies with the pod.

Ships INERT-BUT-HEALTHY with zero peers. THREE off-repo manual steps remain
(kernel module, server key, WAN forward) -- runbooks/vpn-remote-access.md.

Touches clusters/** , so ci/approval-policy.sh will block pending the
operator's /approve-override. Deliberately not posted by me (CLAUDE.md §1).

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

clusters/base/kustomization.yaml

@@ -71,4 +71,11 @@ resources:
   # controller must NEVER gate the platform chain; same non-gating rationale as headlamp/oauth2-proxy.
   # Carries velero-cloud.sops.yaml, so clusters/dev adds a SOPS decryption patch for it (by name).
   - backup.yaml          # Flux Kustomization -> ./platform/velero (dependsOn platform-config)
+  # WireGuard remote-access VPN (north-south INGRESS, udp/51820) — POST-platform tier
+  # (dependsOn platform-config, wait:false). NOT the same thing as platform/vpn-egress, which sends
+  # pods OUT through PIA; this lets remote CLIENTS IN. Non-gating is load-bearing rather than
+  # conventional here: its DaemonSet cannot start until the operator creates the out-of-band
+  # `wg-server-key` Secret, so in the gating `platform` tier an unfinished manual step would have
+  # stalled every apps wave. Carries no SOPS secret, so neither overlay adds a decryption patch.
+  - vpn-ingress.yaml     # Flux Kustomization -> ./platform/vpn-ingress (dependsOn platform-config)
   - cluster-vars.yaml    # overlay knob surface (base defaults)