transport/ethernet: rename config discovery flag to listen

Rename the Ethernet per-interface config flag from discovery to listen,
so the receive/transmit toggle pair reads as the symmetric announce
(transmit) / listen (receive) neighbor-beacon vocabulary. The old
discovery: key is still accepted via a serde alias, so deployed configs
load unchanged; to_yaml re-emits it under the canonical listen: name.
Marked deprecated for removal at the v2 cutover.

Updates the config field + accessor, the transport listen_enabled local,
the one struct-literal test consumer, the chaos sim config generator,
packaged fips.yaml examples, and the classified operator-facing docs
(ethernet neighbor-beacon subsystem prose; the generic Transport
discovery capability prose is left unchanged). Adds a compat parse test
asserting the legacy alias, the new key, and that deny_unknown_fields
still rejects unknown keys. Behavior-neutral.

docs/reference/configuration.md

@@ -436,7 +436,7 @@ Requires `CAP_NET_RAW` or running as root. Linux only.
 | `mtu` | u16 | *(auto)* | Override MTU. Default: interface MTU minus 3 (for frame type + length prefix) |
 | `recv_buf_size` | usize | `2097152` | Socket receive buffer size in bytes (2 MB) |
 | `send_buf_size` | usize | `2097152` | Socket send buffer size in bytes (2 MB) |
-| `discovery` | bool | `true` | Listen for discovery beacons from other nodes |
+| `listen` | bool | `true` | Listen for neighbor beacons from other nodes |
 | `announce` | bool | `false` | Broadcast announcement beacons on the LAN |
 | `auto_connect` | bool | `false` | Auto-connect to discovered peers |
 | `accept_connections` | bool | `false` | Accept incoming connection attempts from discovered peers |
@@ -450,7 +450,7 @@ transports:
   ethernet:
     lan:
       interface: "eth0"
-      discovery: true
+      listen: true
       announce: true
     backbone:
       interface: "eth1"
@@ -458,7 +458,7 @@ transports:
 ```
 
 Each named instance operates independently with its own socket and
-discovery state. The instance name is used in log messages and the
+neighbor state. The instance name is used in log messages and the
 `name()` method on the Transport trait.
 
 ### TCP (`transports.tcp.*`)
@@ -840,7 +840,7 @@ peers:
 ### Mixed UDP + Ethernet Example
 
 A node bridging internet peers (UDP) and a local Ethernet segment with
-beacon discovery:
+neighbor beacons:
 
 ```yaml
 node:
@@ -856,7 +856,7 @@ transports:
     mtu: 1472
   ethernet:
     interface: "eth0"
-    discovery: true
+    listen: true
     announce: true
     auto_connect: true
     accept_connections: true
@@ -999,7 +999,7 @@ transports:
   #   mtu: null                      # null = interface MTU - 3 (typically 1497)
   #   recv_buf_size: 2097152         # 2 MB
   #   send_buf_size: 2097152         # 2 MB
-  #   discovery: true                # listen for beacons
+  #   listen: true                   # listen for beacons
   #   announce: false                # broadcast beacons
   #   auto_connect: false            # connect to discovered peers
   #   accept_connections: false      # accept inbound handshakes

docs/reference/security.md

@@ -209,7 +209,7 @@ for the metadata-privacy model and the rejection of onion routing.
 | --------- | --------------- | ------------ | ------ |
 | UDP | None until `bind_addr` set | `0.0.0.0:2121` typical | Operator sets `transports.udp.bind_addr` |
 | TCP | None until `bind_addr` set | None — outbound-only without bind | Operator sets `transports.tcp.bind_addr` |
-| Ethernet | Listens on configured interface (raw `AF_PACKET`) | EtherType 0x2121 on selected interface | Per-flag `discovery`, `announce`, `auto_connect`, `accept_connections` |
+| Ethernet | Listens on configured interface (raw `AF_PACKET`) | EtherType 0x2121 on selected interface | Per-flag `listen`, `announce`, `auto_connect`, `accept_connections` |
 | Tor | None until `directory_service` configured | `127.0.0.1:8443` (loopback only) | Operator sets `transports.tor.directory_service` and configures `HiddenServiceDir` in `torrc` |
 | BLE | Off by default | n/a | Operator enables `transports.ble.*` |
 | Nostr discovery | Off by default | n/a (relay client, not a listener) | Operator sets `node.discovery.nostr.enabled: true` |