M1 step 6: Wi-Fi Tools from ordinary scans

- lib/wifi (host-tested): channel occupancy (neighbour spill, signal
  weighting, quietest of 1/6/11) and a signal tracker (history, lost
  detection, click interval)
- WifiService: scan results carry BSSID, channel and security; a scan
  can target one channel for quick tracker refreshes; endListScans()
  turns the radio back off when Wi-Fi is disabled
- Wi-Fi Tools App: networks nearby, channel occupancy bars, signal
  tracker with clicks (m to mute)
- M1 plan: Monitoring-mode views and captures deferred

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

lib/wifi/src/channel_occupancy.h

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <array>
+#include <vector>
+
+namespace roro {
+
+struct ChannelSighting {
+    int channel;
+    int rssi;
+};
+
+// How crowded each 2.4 GHz Wi-Fi channel (1..13) is, from the access points a scan saw. A 20 MHz
+// network spills onto the channels up to two away, less the further it is; a strong signal
+// counts more than a faint one. Index 0 is unused.
+std::array<float, 14> channelLoad(const std::vector<ChannelSighting>& sightings);
+
+// The least crowded of the non-overlapping channels 1, 6 and 11 (the lowest on a tie).
+int quietestChannel(const std::array<float, 14>& load);
+
+}  // namespace roro