feat: settings ops, the WiFi and frequency scans, and reboot for socket protocol 2

Step 1d of the protocol 2 core (docs/SECURITY_PLAN.md).

- getSettings/saveSettings by section: general, network, mqtt, security,
  radio. A save is the settings route's request, so loop() applies it with
  the settings' own fromJSON(). ProtoSettings checks every field first:
  kind, range, string length, IP addresses.
- Secrets are only reported as has*. A security save replies with the
  client's new token and closes the other sockets; other saves send
  settingsChanged to the other clients.
- scanWifi runs an async scan from ESPNetwork, kept apart from the roaming
  scan, and wifiNetworks goes to the clients that asked.
- beginFrequencyScan, endFrequencyScan and reboot run at once on async_tcp,
  as their routes do: a scan's end mustn't wait in the loop queue behind an
  unpair that waits for the scan to end (new op kind 'a').
- e2e: test_settings.py and a --reboot flag.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/SECURITY_PLAN.md

@@ -37,6 +37,7 @@
 - **Handshake:** the socket is `ws://host/ws` on port 80. The token goes in `?apikey=<token>`, because browsers can't set headers on a websocket. `handleHandshake` checks it with the same comparison the HTTP routes use. `request->url()` is the path only, so the token doesn't reach the slow-request log.
 - **Rules:** under None anyone can connect. Under Secured the handshake needs a valid token, and a connection that has one may send every op and subscribe to every feed.
 - **Logging in with a socket already open:** the UI reconnects the socket with the token. There is no in-band upgrade message.
+- **Changing the security settings:** a `saveSettings` of the security section closes every other socket, since their tokens may no longer be good, and a socket opened under None had none. They connect again and log in when refused. The client that saved gets its new token in the reply.
 - **Origin:** a handshake whose `Origin` header doesn't match `Host` is refused.
 
 ### CORS