Add opt-in WireGuard mesh support to services.hyperhive.swarm:
- swarm.peers.<domain>.wireguardPublicKey — peer's wg public key
- swarm.peers.<domain>.wireguardEndpoint — peer's UDP endpoint (optional)
- swarm.peers.<domain>.wireguardAddress — peer's mesh IP with prefix
- swarm.wireguard.enable — bring up wg-hive interface
- swarm.wireguard.privateKeyFile — path to host's wg private key
- swarm.wireguard.address — this host's mesh IP/prefix
- swarm.wireguard.listenPort — UDP listen port (default 51820)
- swarm.wireguard.persistentKeepalive — keepalive seconds (default 25)
When enabled, generates networking.wireguard.interfaces.wg-hive with
one peer entry per mesh-enabled swarm.peers entry. Opens listenPort
UDP on the host firewall. Adds wireguard_address to HYPERHIVE_PEERS
JSON so hive-c0re can use mesh IPs for intra-swarm routing.
Assertions guard against enable=true without privateKeyFile or address.
Also refactors networking.firewall.allowedTCPPortRanges from the
nested attrset form (which conflicted with the new allowedUDPPorts
line) to the per-attribute form.
docs/swarm.md: adds WireGuard setup section with key generation
commands, two-hive config example, NAT/keepalive notes.
