Add BT1035 driver with manual chapter and expand Si4684 tuning docs.

Implement Bt1035Driver AT init (AT+AUXCFG=1), core AT parser with host tests,
wire boot into HardwareBootstrap, and document DAB/FM tuning workflows in ch-si4684.

Co-authored-by: Cursor <cursoragent@cursor.com>

Software/components/core/test/CMakeLists.txt

@@ -34,6 +34,7 @@ add_library(digiradio_core STATIC
     "${CORE_SRC_DIR}/EnhancementsDesign.cpp"
     "${CORE_SRC_DIR}/AudioProfile.cpp"
     "${CORE_SRC_DIR}/AudioProfileJson.cpp"
+    "${CORE_SRC_DIR}/Bt1035At.cpp"
 )
 target_include_directories(digiradio_core PUBLIC
     "${CMAKE_CURRENT_SOURCE_DIR}/../include"
@@ -70,3 +71,7 @@ add_test(NAME audio_profile_json_test COMMAND audio_profile_json_test)
 add_executable(enhancements_design_test enhancements_design_test.cpp)
 target_link_libraries(enhancements_design_test PRIVATE digiradio_core)
 add_test(NAME enhancements_design_test COMMAND enhancements_design_test)
+
+add_executable(bt1035_at_test bt1035_at_test.cpp)
+target_link_libraries(bt1035_at_test PRIVATE digiradio_core)
+add_test(NAME bt1035_at_test COMMAND bt1035_at_test)

Software/components/core/test/bt1035_at_test.cpp

@@ -0,0 +1,71 @@
+/**
+ * @file    bt1035_at_test.cpp
+ * @brief   Host tests for FSC-BT1035 AT command builder and parser.
+ *
+ * DigiRadio firmware — https://github.com/manvalan/DigiRadio
+ *
+ * Copyright 2026 Michele Bigi
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * @author  Michele Bigi
+ * @date    2026-07-06
+ */
+
+#include "core/Bt1035At.hpp"
+
+#include <cstdlib>
+#include <iostream>
+#include <string>
+
+namespace {
+
+[[nodiscard]] int runInitSequenceTest()
+{
+    const auto sequence = core::bootInitSequence();
+    if (sequence.size() != core::kBt1035BootInitCommandCount) {
+        std::cerr << "init sequence size mismatch\n";
+        return EXIT_FAILURE;
+    }
+    if (sequence[1U] != core::Bt1035AtCommand::AuxLineIn) {
+        std::cerr << "AUXCFG=1 must be in init sequence\n";
+        return EXIT_FAILURE;
+    }
+    const std::string aux = core::buildBt1035AtLine(core::Bt1035AtCommand::AuxLineIn);
+    if (aux != "AT+AUXCFG=1\r\n") {
+        std::cerr << "AUXCFG command line mismatch\n";
+        return EXIT_FAILURE;
+    }
+    return EXIT_SUCCESS;
+}
+
+[[nodiscard]] int runParseTest()
+{
+    if (core::parseBt1035AtResponse("OK\r\n") != core::Bt1035AtResponseKind::Ok) {
+        std::cerr << "OK parse failed\n";
+        return EXIT_FAILURE;
+    }
+    if (core::parseBt1035AtResponse("ERROR\r\n")
+        != core::Bt1035AtResponseKind::Error) {
+        std::cerr << "ERROR parse failed\n";
+        return EXIT_FAILURE;
+    }
+    if (core::parseBt1035AtResponse("garbage")
+        != core::Bt1035AtResponseKind::Unexpected) {
+        std::cerr << "unexpected parse failed\n";
+        return EXIT_FAILURE;
+    }
+    return EXIT_SUCCESS;
+}
+
+} // namespace
+
+int main()
+{
+    if (runInitSequenceTest() != EXIT_SUCCESS) {
+        return EXIT_FAILURE;
+    }
+    if (runParseTest() != EXIT_SUCCESS) {
+        return EXIT_FAILURE;
+    }
+    return EXIT_SUCCESS;
+}