Add internet radio streaming with runtime API, modernize web UI, remove auto-tune/beep at boot

Streaming (main feature this session):
- New WebRadioConfig/WebRadioJson core types, ISecureStore-backed persistence
- New webradio::WebRadioService (thread-safe live config) + GET/POST /api/streaming
- web_radio_stream task now runtime-toggleable (no reboot), no hardcoded URL
- Content-Type diagnostic: warns clearly when a URL is a webpage, not an audio stream

Boot cleanup:
- Removed boot-time auto FM/DAB tune, auto-beep, and the (now-concluded) Si4684
  crystal IBIAS/CTUN empirical sweep from main.cpp — tuning/beep are on-demand
  via the existing REST API only

Web UI:
- Modernized styling (cards, gradients, toggle switches, light/dark theme)
- New Stream tab wired to /api/streaming

Fixes found via real idf.py build (not just clangd):
- Restored wrongly-removed si4684/Si4684Tuner.hpp include in main.cpp
- Fixed MP3Decode() argument types in web_radio_stream.cpp (unsigned char**/int*)

Quality-gate fixes:
- Host-test stub headers (esp_log.h, freertos/*) so TunerService.cpp's
  scanForStation logging/pacing compiles for station_service_test /
  integration_service_test instead of running stale binaries
- Added WifiScanner and WebRadioService manual sections; filled in missing
  Doxygen docs on BluetoothService, i2s_sdata_probe, test_firmware, Bt1035At
- Ignore clangd's .cache/ index directory

Also includes prior uncommitted work carried in the tree: Wi-Fi/Bluetooth
device scan REST API and UI (WifiScanner, BT scan), SigmaStudio TCP bridge,
and the current ADAU1701 SigmaStudio DSP program export.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Software/main/hardware_bootstrap.cpp

@@ -75,8 +75,6 @@ bt1035::Bt1035Driver gBt1035(
     bt1035::Bt1035Pins{
         .uartTx = board::pins::Bt1035UartTx,
         .uartRx = board::pins::Bt1035UartRx,
-        .rtsGpio = board::pins::Bt1035Rts,
-        .ctsGpio = board::pins::Bt1035Cts,
         .resetGpio = board::pins::Bt1035Reset,
         .sysCtlGpio = board::pins::Bt1035SysCtl,
     });
@@ -122,6 +120,11 @@ std::expected<void, HardwareBootError> HardwareBootstrap::boot()
     if (auto audioResult = gAudioService.loadAndApply(); !audioResult) {
         ESP_LOGW(kTag, "ADAU1701 profile apply failed");
     }
+    if (auto radioMix = gAudioService.applyRadioFirstMix(false); !radioMix) {
+        ESP_LOGW(kTag, "ADAU1701 radio-first mix failed");
+    } else {
+        ESP_LOGI(kTag, "ADAU1701 Si4684 input routed (radio-first mix)");
+    }
 
     if (auto btResult = gBt1035.boot(); !btResult) {
         ESP_LOGE(kTag, "BT1035 boot failed");