docs(wireguard): bring the management hub up and prove it end-to-end

The hub lives in queue-provisioning (the only worker on the provisioning queue,
and LocalWireguardHub shells out to wg in-process). Generated the hub keypair,
wrote wg0.conf, and filled CLUPILOT_WG_ENDPOINT/HUB_PUBKEY.

Verified against the running stack rather than mocks: registered a stand-in
Proxmox peer through the app's own addPeer(), got a handshake, opened hub->peer
TCP over the tunnel (what the SSH steps actually need — a handshake alone does
not prove routed TCP), confirmed wg-quick save persisted the peer, then removed
it through removePeer(). wg0 returns after a container restart.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/wireguard-hub.md

@@ -0,0 +1,85 @@
+# WireGuard management hub
+
+Every Proxmox host CluPilot manages is reachable **only** over this tunnel — the
+hosts have no public SSH. The hub is the one endpoint that accepts peers.
+
+## Where it runs
+
+Inside the `queue-provisioning` container, not on the VM host. That container is
+the only one that needs it: `AdvanceRunJob`, `PurgeHost` and `RemoveWireguardPeer`
+all `onQueue('provisioning')`, and it is the only worker consuming that queue.
+`LocalWireguardHub` shells out to `wg` / `wg-quick`, so the interface must exist
+in the same namespace as the PHP process.
+
+Compose already grants what that needs: `cap_add: NET_ADMIN`, `/dev/net/tun`,
+`net.ipv4.ip_forward=1`, the published `51820/udp`, and a named `wireguard`
+volume for `/etc/wireguard`. The container command runs `wg-quick up wg0` before
+the worker starts, so the tunnel returns after every restart.
+
+The host kernel module does not need `modprobe`: creating the first
+`type wireguard` link auto-loads `wireguard.ko`.
+
+## First-time setup
+
+Only needed when the `wireguard` volume is empty (the config is not in git — it
+holds the private key).
+
+```bash
+docker compose exec queue-provisioning sh -c 'umask 077; wg genkey > /etc/wireguard/hub.key; wg pubkey < /etc/wireguard/hub.key'
+```
+
+Write `/etc/wireguard/wg0.conf` with that private key:
+
+```ini
+[Interface]
+Address = 10.66.0.1/24
+ListenPort = 51820
+PrivateKey = <hub.key>
+```
+
+Then set in `.env` — `CLUPILOT_WG_ENDPOINT` must be the address a **Proxmox host**
+can reach, not a container address:
+
+```
+CLUPILOT_WG_ENDPOINT=10.10.90.185:51820
+CLUPILOT_WG_HUB_PUBKEY=<the pubkey printed above>
+```
+
+`wg-quick save wg0` rewrites `wg0.conf` on every peer change, so keep manual
+edits to a minimum — comments in that file are lost.
+
+## Peer lifecycle
+
+`LocalWireguardHub::allocateIp()` hands out the next free address in
+`CLUPILOT_WG_SUBNET`, skipping the hub IP, the network and the broadcast address,
+and skipping every `hosts.wg_ip` already taken. `addPeer()`/`removePeer()` run
+`wg set` and then `wg-quick save wg0` — without the save, peers are lost on the
+next restart.
+
+## Verifying it actually works
+
+Mocked tests cannot prove a tunnel. Against the running stack:
+
+1. Start a throwaway peer that stands in for a Proxmox host:
+   `docker run -d --name wgpeer --cap-add NET_ADMIN --device /dev/net/tun clupilot-app:dev sleep 900`
+2. Generate its keypair, register it through the app (not by hand) —
+   `app(WireguardHub::class)->addPeer('<peer pubkey>', '10.66.0.2')`.
+3. Bring up the peer with `Endpoint = 10.10.90.185:51820`,
+   `AllowedIPs = 10.66.0.0/24`, `PersistentKeepalive = 25`.
+4. `wg show wg0` on both sides must report a recent handshake.
+5. Prove the direction the pipeline needs — hub → peer TCP, which is what the SSH
+   steps use: listen on `10.66.0.2:2222` in the peer and `fsockopen` to it from
+   `queue-provisioning`. A handshake alone does not prove routed TCP.
+6. Clean up with `removePeer()` and delete the container.
+
+Verified end-to-end on 2026-07-25: handshake established, hub→peer TCP banner
+received, peer persisted to `wg0.conf` by `wg-quick save` and removed again.
+
+## Before production
+
+- The endpoint becomes the production VM's address; regenerate the keypair there
+  (the dev private key must never travel).
+- `51820/udp` is the only port that has to be open inbound — the console and the
+  Proxmox hosts stay off the public hostnames (see `config/admin_access.php`).
+- Back up `/etc/wireguard/` (the `wireguard` volume): losing the hub private key
+  means re-peering every host.