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

src/services/wifi_service.h

@@ -12,9 +12,12 @@
 namespace roro {
 
 struct ScanEntry {
-    std::string ssid;
+    std::string ssid;  // empty for a hidden network
+    std::string bssid;
+    int channel;
     int rssi;
     bool open;
+    std::string security;  // "open", "WPA2", "WPA3"...
 };
 
 // Owns the Wi-Fi radio: carries out the WifiController's decisions with the ESP32 Wi-Fi stack,
@@ -31,10 +34,14 @@ class WifiService : public Service {
     const std::string& ssid() const { return controller_.ssid(); }
     int rssi() const;
 
-    // Scan for the "add a network" list; results arrive in listScan() when listScanDone().
-    void startListScan();
+    // Scans for a list of nearby networks (all channels, or just one for a quick refresh); results
+    // arrive in listScan() when listScanDone(), and listScanSeq() counts completed scans.
+    void startListScan(int channel = 0);
     bool listScanDone() const { return !listScanPending_; }
     const std::vector<ScanEntry>& listScan() const { return listScan_; }
+    uint32_t listScanSeq() const { return listScanSeq_; }
+    // Done with list scans: switch the radio back off if Wi-Fi itself is off.
+    void endListScans();
 
     // A Saved Network was added: try it now rather than after the retry delay.
     void savedNetworksChanged() { controller_.retryNow(millis()); }
@@ -44,7 +51,7 @@ class WifiService : public Service {
 
    private:
     void apply(const WifiController::Step& step);
-    void startScan();
+    void startScan(int channel = 0);
     void finishScan(uint32_t nowMs);
     void startNtp();
 
@@ -55,6 +62,7 @@ class WifiService : public Service {
     bool scanRunning_ = false;
     bool listScanPending_ = false;
     std::vector<ScanEntry> listScan_;
+    uint32_t listScanSeq_ = 0;
     bool ntpWaiting_ = false;
     bool radioInitialised_ = false;
 };