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>

test/e2e/conftest.py

@@ -18,6 +18,7 @@ def pytest_addoption(parser):
     parser.addoption("--radio", action="store_true", help="also run the tests that send commands on air")
     parser.addoption("--shade", type=int, default=None, help="with --radio: the id of the shade the commands may move")
     parser.addoption("--edit", action="store_true", help="also run the edits that change the shade model, then undo them")
+    parser.addoption("--reboot", action="store_true", help="also run the test that reboots the device")
 
 
 @pytest.fixture(scope="session")