M3 step 5: Sweep, the band's signal strength as bars and a waterfall

Tab in the LoRa Scanner sweeps 863-870 MHz in 100 kHz steps (the
strongest of three RSSI readings at each, at 125 kHz), shown as bars with
peak hold over a waterfall, the Sniffer's frequency marked (Q98). The
Sweep pauses the Sniffer and keeps its packets; Tab resumes it (Q99).
Status Bar: SW. The floor, top and peaks are host-tested; `lora sweep
on|off|dump` prints them on the console.

At the desk: about 607 ms a pass, a flat floor at -100 to -102 dBm
(15 dB above the chip's own) and a steady carrier at 863.2 MHz.

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

lib/lora/src/sweep_view.h

@@ -0,0 +1,27 @@
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+#include <vector>
+
+namespace roro::lora {
+
+// What a Sweep pass says about the band (M3, Q98): one RSSI reading (dBm) per step.
+struct SweepPeak {
+    uint32_t hz;
+    int dbm;
+};
+struct SweepStats {
+    int floor = 0;  // the median: the band's noise floor, whatever a few signals do
+    int top = 0;    // the strongest reading
+    std::vector<SweepPeak> peaks;  // at most 3, strongest first, each a local maximum >= 10 dB above the floor
+};
+
+SweepStats summarize(const int8_t* dbm, size_t steps, uint32_t fromHz, uint32_t stepHz);
+
+// The waterfall's colours: a reading between `low` and `high` dBm as 0..255, then RGB565 along
+// black, blue, cyan, green, yellow, red.
+uint8_t heatLevel(int dbm, int low, int high);
+uint16_t heatColor(uint8_t level);
+
+}  // namespace roro::lora