Add full FM band scan for building a station/channel list

New TunerService::scanFullFmBand(): tunes to the band bottom then seeks up
repeatedly (reusing the existing hardware-seek + RDS-name-poll machinery
from scanForStation()) until the sweep wraps back around, collecting every
station that clears the existing scan RSSI/SNR thresholds. Returns the
list without touching saved presets or leaving the tuner in any particular
place — callers decide what to do with the results.

New POST /api/tuner/scan/full endpoint (core::TunerFmScannedStation DTO,
serializeTunerFmBandScanJson). Blocks for the whole sweep like the existing
/api/tuner/scan.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0178rASQ6ZETPMUamvpoR2KR

Software/components/core/include/core/TunerJson.hpp

@@ -95,6 +95,23 @@ struct TunerScanResult {
     std::optional<BroadcastLabel> stationName;    ///< RDS PS or DAB label when known.
 };
 
+/**
+ * @brief    TunerFmScannedStation — one hit from a full FM band scan.
+ *
+ * @dname    TunerFmScannedStation
+ * @return   n/a (type)
+ * @pubstate Plain DTO built by TunerService::scanFullFmBand().
+ *
+ * @author   Michele Bigi
+ * @date     2026-08-18
+ */
+struct TunerFmScannedStation {
+    FrequencyKHz frequency;              ///< Centre frequency of the hit.
+    std::int8_t rssiDbuV;                ///< RSSI at the time of the hit.
+    std::int8_t snrDb;                   ///< SNR at the time of the hit.
+    std::optional<BroadcastLabel> stationName; ///< RDS PS name, if decoded in time.
+};
+
 /**
  * @brief    serializeTunerStatusJson — serialise a tuner snapshot for GET status.
  *
@@ -207,4 +224,19 @@ struct TunerScanResult {
  */
 [[nodiscard]] std::string serializeTunerScanJson(const TunerScanResult& result);
 
+/**
+ * @brief    serializeTunerFmBandScanJson — serialise a full FM band scan.
+ *
+ * @dname    serializeTunerFmBandScanJson
+ * @param    stations  Hits from TunerService::scanFullFmBand(), in the
+ *                      order the sweep found them (ascending frequency).
+ * @return   JSON object with a `stations` array for the HTTP response body.
+ * @pubstate none
+ *
+ * @author   Michele Bigi
+ * @date     2026-08-18
+ */
+[[nodiscard]] std::string serializeTunerFmBandScanJson(
+    const std::vector<TunerFmScannedStation>& stations);
+
 } // namespace core

Software/components/core/src/TunerJson.cpp

@@ -316,4 +316,24 @@ std::string serializeTunerScanJson(const TunerScanResult& result)
     return out.str();
 }
 
+std::string serializeTunerFmBandScanJson(
+    const std::vector<TunerFmScannedStation>& stations)
+{
+    std::ostringstream out;
+    out << "{\"stations\":[";
+    for (std::size_t i = 0; i < stations.size(); ++i) {
+        if (i > 0U) {
+            out << ',';
+        }
+        const auto& s = stations[i];
+        out << "{\"frequency_khz\":" << s.frequency.value()
+            << ",\"rssi_dbuv\":" << static_cast<int>(s.rssiDbuV)
+            << ",\"snr_db\":" << static_cast<int>(s.snrDb);
+        appendOptionalLabel(out, "station_name", s.stationName);
+        out << "}";
+    }
+    out << "]}";
+    return out.str();
+}
+
 } // namespace core

Software/components/core/test/tuner_json_test.cpp

@@ -139,6 +139,29 @@ namespace {
     return EXIT_SUCCESS;
 }
 
+[[nodiscard]] int runTunerFmBandScanSerialiseTest()
+{
+    core::TunerFmScannedStation withName{
+        *core::FrequencyKHz::tryFromKhz(98300U), 12, 13,
+        core::BroadcastLabel::tryFromChipBytes("RADIO 1")};
+    core::TunerFmScannedStation withoutName{
+        *core::FrequencyKHz::tryFromKhz(105500U), -4, -2, std::nullopt};
+
+    const std::string json =
+        core::serializeTunerFmBandScanJson({withName, withoutName});
+    if (!expectEqual(
+            json,
+            R"({"stations":[{"frequency_khz":98300,"rssi_dbuv":12,"snr_db":13,"station_name":"RADIO 1"},{"frequency_khz":105500,"rssi_dbuv":-4,"snr_db":-2}]})")) {
+        return EXIT_FAILURE;
+    }
+
+    const std::string emptyJson = core::serializeTunerFmBandScanJson({});
+    if (!expectEqual(emptyJson, R"({"stations":[]})")) {
+        return EXIT_FAILURE;
+    }
+    return EXIT_SUCCESS;
+}
+
 [[nodiscard]] int runTunerStatusMetadataSerialiseTest()
 {
     core::TunerStatus status = {};
@@ -240,5 +263,8 @@ int main()
     if (runTunerSeekParseTest() != EXIT_SUCCESS) {
         return EXIT_FAILURE;
     }
+    if (runTunerFmBandScanSerialiseTest() != EXIT_SUCCESS) {
+        return EXIT_FAILURE;
+    }
     return EXIT_SUCCESS;
 }