Add FM ANTCAP antenna calibration: HTTP sweep control + EEPROM persistence

Confirmed live tonight that the Si4684's automatic front-end tuning
(FE_VARM/VARB properties) is measurably suboptimal on this board: a
129-value ANTCAP sweep (0-128, AN851 Appendix A) at four different FM
frequencies found antcap=102 beats auto-tune by +6 to +11 dB RSSI and
+3 to +11 dB SNR everywhere tested, consistent with the front-end
network component mismatch already logged in
docs/si4684-rf-investigation-report.md — the board's actual matching
network differs from the AN851 reference network those auto-tune
constants were derived from, so a fixed empirical override
compensates for a gap the chip's own algorithm can't see.

Wiring, bottom to top:
- Si4684Driver::tuneFm() already took an antCap byte; threaded it
  through core::ITuner::tuneFm() and si4684::Si4684Tuner::tuneFm() as
  a new parameter (default 0 = auto, unchanged behaviour for every
  existing caller).
- TunerService::tuneFm() takes an optional override instead: omitted,
  it falls back to a new defaultFmAntCap_ member so every ordinary FM
  tune (seek, scan, station recall, live UI) benefits automatically
  once calibrated, not just calls that pass antcap explicitly.
- POST /api/tuner/tune gained an optional "antcap" field for sweeping
  live without touching the saved calibration.
- POST /api/tuner/calibrate-antenna commits a sweep result: writes it
  to the 24AA025E48 EEPROM's user-writable region (word address 0x00,
  separate from the factory-locked EUI-48 at 0xFA-0xFF) via a new
  Eeprom24aa::writeFmAntCap()/readFmAntCap() pair, and immediately
  updates the live TunerService default — no reboot needed to take
  effect, though HardwareBootstrap::boot() also loads it at every
  boot so it survives power cycles. Same net::AntennaCalibration
  function-pointer bridge pattern as PhoneStreamSink/BleProvisioning,
  so components/net stays free of eeprom24aa headers.

Verified end to end on hardware: swept and found 102, saved it via
the new endpoint, confirmed the live default changed immediately,
then power-cycled and confirmed the boot log reports "FM ANTCAP
calibration loaded: 102" and a subsequent default tune reflects it.

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

Software/components/net/include/net/NetBootstrap.hpp

@@ -87,6 +87,8 @@ public:
      * @param    ota             Firmware OTA service for POST /api/system/ota.
      * @param    webRadio        Streaming config for GET/POST /api/streaming.
      * @param    phoneStream     I2S write-through for PUT /api/stream/phone.
+     * @param    antennaCalibration  EEPROM write-through for
+     *                                POST /api/tuner/calibrate-antenna.
      * @param    companionChips  Boot flags exposed on GET /api/health.
      * @param    deviceIdentity  EEPROM-derived SSID, hostname, and serial.
      * @return   NetBootstrap on success, or a NetError.
@@ -103,6 +105,7 @@ public:
           ota::OtaService& ota,
           webradio::WebRadioService& webRadio,
           PhoneStreamSink& phoneStream,
+          AntennaCalibration& antennaCalibration,
           core::CompanionChipStatus companionChips,
           const core::DeviceIdentity& deviceIdentity);
 

Software/components/net/include/net/SetupWebServer.hpp

@@ -85,6 +85,25 @@ struct PhoneStreamSink {
                              std::size_t frameCount);
 };
 
+/**
+ * @brief    AntennaCalibration — plain function pointer over EEPROM-backed
+ *           FM ANTCAP storage, so net/ never includes eeprom24aa headers
+ *           directly; main/ supplies it (HardwareBootstrap owns the I2C
+ *           bus and EEPROM handle).
+ *
+ * @dname    AntennaCalibration
+ * @return   n/a (type)
+ * @pubstate Free function with process lifetime; no per-instance state.
+ *
+ * @author   Michele Bigi
+ * @date     2026-08-19
+ */
+struct AntennaCalibration {
+    /** Persist a new FM ANTCAP calibration value to EEPROM.
+     *  @return false on an I2C failure. */
+    bool (*save)(std::uint8_t antCap);
+};
+
 /**
  * @brief    HttpRouteContext — dependencies injected into HTTP handlers.
  *
@@ -106,6 +125,7 @@ struct HttpRouteContext {
     ota::OtaService* ota;                         ///< Firmware OTA streaming.
     webradio::WebRadioService* webRadio; ///< Streaming config REST routes.
     PhoneStreamSink* phoneStream; ///< PUT /api/stream/phone I2S write-through.
+    AntennaCalibration* antennaCalibration; ///< POST /api/tuner/calibrate-antenna.
     core::CompanionChipStatus companionChips; ///< Boot flags for /api/health.
     core::DeviceIdentity deviceIdentity;       ///< EEPROM-derived unit identity.
 };
@@ -187,6 +207,8 @@ public:
      * @param    ota             Firmware OTA service for POST /api/system/ota.
      * @param    webRadio        Streaming config for GET/POST /api/streaming.
      * @param    phoneStream     I2S write-through for PUT /api/stream/phone.
+     * @param    antennaCalibration  EEPROM write-through for
+     *                                POST /api/tuner/calibrate-antenna.
      * @param    companionChips  Boot flags for GET /api/health.
      * @param    deviceIdentity  Unit identity for /api/health serialNumber.
      * @return   Ok on success, or NetError::HttpServerStartFailed.
@@ -204,6 +226,7 @@ public:
         ota::OtaService& ota,
         webradio::WebRadioService& webRadio,
         PhoneStreamSink& phoneStream,
+        AntennaCalibration& antennaCalibration,
         core::CompanionChipStatus companionChips,
         const core::DeviceIdentity& deviceIdentity);