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/src/NetBootstrap.cpp

@@ -106,6 +106,7 @@ startSetupMode(core::ISecureStore& store, tuner::TunerService& tuner,
                ota::OtaService& ota,
                webradio::WebRadioService& webRadio,
                PhoneStreamSink& phoneStream,
+               AntennaCalibration& antennaCalibration,
                core::CompanionChipStatus companionChips,
                const core::DeviceIdentity& deviceIdentity)
 {
@@ -121,7 +122,8 @@ startSetupMode(core::ISecureStore& store, tuner::TunerService& tuner,
     if (auto webResult =
             webServer.start(store, NetState::SoftApSetup, tuner, audio,
                             bluetooth, stations, integration, ota, webRadio,
-                            phoneStream, companionChips, deviceIdentity);
+                            phoneStream, antennaCalibration, companionChips,
+                            deviceIdentity);
         !webResult) {
         return std::unexpected(webResult.error());
     }
@@ -168,6 +170,7 @@ startStaMode(core::ISecureStore& store, tuner::TunerService& tuner,
              ota::OtaService& ota,
              webradio::WebRadioService& webRadio,
              PhoneStreamSink& phoneStream,
+             AntennaCalibration& antennaCalibration,
              core::CompanionChipStatus companionChips,
              const core::DeviceIdentity& deviceIdentity)
 {
@@ -198,7 +201,8 @@ startStaMode(core::ISecureStore& store, tuner::TunerService& tuner,
     if (auto webResult =
             webServer.start(store, NetState::StaConnected, tuner, audio,
                             bluetooth, stations, integration, ota, webRadio,
-                            phoneStream, companionChips, deviceIdentity);
+                            phoneStream, antennaCalibration, companionChips,
+                            deviceIdentity);
         !webResult) {
         return std::unexpected(webResult.error());
     }
@@ -227,6 +231,7 @@ NetBootstrap::start(core::ISecureStore& store, tuner::TunerService& tuner,
                     ota::OtaService& ota,
                     webradio::WebRadioService& webRadio,
                     PhoneStreamSink& phoneStream,
+                    AntennaCalibration& antennaCalibration,
                     core::CompanionChipStatus companionChips,
                     const core::DeviceIdentity& deviceIdentity)
 {
@@ -241,7 +246,8 @@ NetBootstrap::start(core::ISecureStore& store, tuner::TunerService& tuner,
     if (store.hasWifiCredentials()) {
         auto staResult = startStaMode(store, tuner, audio, bluetooth, stations,
                                       integration, ota, webRadio, phoneStream,
-                                      companionChips, deviceIdentity);
+                                      antennaCalibration, companionChips,
+                                      deviceIdentity);
         if (staResult) {
             return staResult;
         }
@@ -253,8 +259,8 @@ NetBootstrap::start(core::ISecureStore& store, tuner::TunerService& tuner,
     }
 
     return startSetupMode(store, tuner, audio, bluetooth, stations, integration,
-                          ota, webRadio, phoneStream, companionChips,
-                          deviceIdentity);
+                          ota, webRadio, phoneStream, antennaCalibration,
+                          companionChips, deviceIdentity);
 }
 
 NetBootstrap::NetBootstrap(std::optional<SoftApHost> softAp,