fix(vpn-ingress): content-hash the peer register, or a merged peer never reaches the tunnel

The operator enrolled a phone, merged the peer, and `wg show` listed none.
Measured on prod 2026-10-06 with the peer already on main:

  live wg-peers ConfigMap, active AllowedIPs .. 0
  DaemonSet volume reference ................. configMap.name: wg-peers (FIXED)
  DaemonSet generation/observedGeneration .... 1 / 1   (never rolled)
  init container, all three pods ............. "0 peer(s)"

Part of it was just the 10m reconcile interval. The defect is the fixed name:
Flux updates a fixed-name ConfigMap IN PLACE, so the pod template is
byte-identical, so no rollout is triggered -- and the init container assembles
wg0.conf ONCE at pod start into a tmpfs, so the running tunnel keeps the old
peer list indefinitely. Adding or revoking a peer had no effect until something
unrelated restarted the pods. For a REVOCATION that is a security defect, not
an inconvenience: delete a stanza, see a green PR, device keeps working.

The runbook and README both claimed "PR -> merge -> Flux rolls the DaemonSet".
Never true. And this repo already documents the fix, in a file I had read --
runbooks/kustomization.yaml: "The generated name carries kustomize's content
hash, so editing any runbook rolls the server automatically and a stale
projection is impossible."

So: peers.yaml (inline ConfigMap) -> peers.conf (plain file) + a
configMapGenerator. The operator's enrolled peer is carried across verbatim.
Every line is WireGuard config and `#` is a legal comment there, so the
documentation now lives inside the file that is actually mounted.

`namespace: vpn-ingress` on the kustomization is REQUIRED, not tidiness: a
generated ConfigMap inherits no namespace, everything else here declares
vpn-ingress, and kustomize's nameReference will not rewrite across a namespace
boundary -- without it the build mounts the unhashed name and the pods wedge on
a missing volume. Caught only by building the output and reading the volumes.

new-peer.sh: PEERS_FILE repointed, and a missing register is now FATAL rather
than skipped -- the old `[ -r "$PEERS_FILE" ] && grep ...` guard meant that
after the rename the only symptom would have been duplicate detection quietly
never firing again. Stale peers.yaml references swept from six files including
the script's own user-facing output.

Verified: the DaemonSet now mounts wg-peers-m9kcckcb5t; the hash tracks content
(edit -> dgg7ht9c74 -> restore -> m9kcckcb5t); the enrolled peer is byte-identical
to main's; and `new-peer.sh dupe 2` is now correctly refused by the operator's
real allocation.

No sensitive paths; merges on a green gate.

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

platform/vpn-ingress/README.md

@@ -13,7 +13,7 @@ egress out the house WAN.
 | Transport | WireGuard, **udp/51820**, kernel implementation |
 | Where it runs | `hostNetwork` **DaemonSet** — one warm listener on every node |
 | Client subnet | `${WG_CLIENT_CIDR}` = `10.90.0.0/24`; `.1` is the server, `.2`–`.254` devices |
-| Authorisation | a device's **public key** is in [`peers.yaml`](./peers.yaml), or it cannot connect |
+| Authorisation | a device's **public key** is in [`peers.conf`](./peers.conf), or it cannot connect |
 | The one secret | the server's private key — **SOPS-encrypted in this tree**, `wg-server-key.sops.yaml` |
 | Exposure | one hand-made WAN port-forward on the SOHO router, off-repo |
 | Enrolling a device | [`infra/vpn-ingress/new-peer.sh`](../../infra/vpn-ingress/new-peer.sh) |
@@ -129,7 +129,7 @@ translations win here.
 
 | half | where | why |
 |---|---|---|
-| peer **public** keys + addresses | [`peers.yaml`](./peers.yaml), **plaintext in git** | a public key grants nothing by itself, and this makes *"who can get into my house"* a reviewable PR diff with `git log` as its audit trail |
+| peer **public** keys + addresses | [`peers.conf`](./peers.conf), **plaintext in git**, as a content-hashed `configMapGenerator` so an edit rolls the pods | a public key grants nothing by itself, and this makes *"who can get into my house"* a reviewable PR diff with `git log` as its audit trail |
 | the server's **private** key | `wg-server-key.sops.yaml`, **SOPS-encrypted in git** | the only real secret (R-SEC-01, spec docs/07). Ships with a `REPLACE-ME` placeholder: an agent must not mint a long-lived private key (CLAUDE.md §6), so the operator `sops set`s it in |
 
 The two are joined only at pod start, by the init container, into a **`medium: Memory` emptyDir** —
@@ -166,8 +166,9 @@ NetworkPolicy applies.
 ## Operating it
 
 * **Enrol a device:** `./infra/vpn-ingress/new-peer.sh <name> <octet>` → paste the printed `[Peer]`
-  stanza into `peers.yaml` → PR → merge. Phones scan a QR code; desktops import a `.conf`.
-* **Revoke a device:** delete its stanza → PR → merge. No other step; the key stops working.
+  stanza into `peers.conf` → PR → merge. Phones scan a QR code; desktops import a `.conf`.
+* **Revoke a device:** delete its stanza from `peers.conf` → PR → merge. No other step; the key
+  stops working as soon as the pods roll (the generator's content hash guarantees they do).
 * **Is it up?** `kubectl --context k3s-prod -n vpn-ingress get ds wireguard` — three Ready.
 * **Who is connected?** `kubectl --context k3s-prod -n vpn-ingress exec ds/wireguard -- wg show`
   (`latest handshake` under ~3 min means live). Never dump `wg showconf` — it prints the private key.
@@ -211,7 +212,7 @@ right way; one was a defect in my own manifest.
   covered generically by `KubeDeploymentReplicasMismatch`/`KubePodNotReady` from
   kube-prometheus-stack. **This is the top follow-up.**
 * **No preshared keys.** They would add a symmetric post-quantum hedge on top of the Noise
-  handshake — and would be a real secret, forcing `peers.yaml` into SOPS and costing the
+  handshake — and would be a real secret, forcing `peers.conf` into SOPS and costing the
   reviewability above. Revisit only if the threat model changes; if it does, the PSK belongs in the
   `wg-server-key` Secret.
 * **No IPv6.** The server offers no IPv6 tunnel address, so a full-tunnel client with native IPv6