feat: AGC phases 4-5 — STM32 outer-loop AGC class + main.cpp integration

Implements the STM32 outer-loop AGC (ADAR1000_AGC) that reads the FPGA
saturation flag on DIG_5/PD13 once per radar frame and adjusts the
ADAR1000 VGA common gain across all 16 RX channels.

Phase 4 — ADAR1000_AGC class (new files):
- ADAR1000_AGC.h/.cpp: attack/recovery/holdoff logic, per-channel
  calibration offsets, effectiveGain() with OOB safety
- test_agc_outer_loop.cpp: 13 tests covering saturation, holdoff,
  recovery, clamping, calibration, SPI spy, reset, mixed sequences

Phase 5 — main.cpp integration:
- Added #include and global outerAgc instance
- AGC update+applyGain call between runRadarPulseSequence() and
  HAL_IWDG_Refresh() in main loop

Build system & shim fixes:
- Makefile: added CXX/CXXFLAGS, C++ object rules, TESTS_WITH_CXX in
  ALL_TESTS (21 total tests)
- stm32_hal_mock.h: const uint8_t* for HAL_UART_Transmit (C++ compat),
  __NOP() macro for host builds
- shims/main.h + real main.h: FPGA_DIG5_SAT pin defines

All tests passing: MCU 21/21, GUI 92/92, cross-layer 29/29.

9_Firmware/9_1_Microcontroller/tests/Makefile

@@ -16,10 +16,17 @@
 ################################################################################
 
 CC       := cc
+CXX      := c++
 CFLAGS   := -std=c11 -Wall -Wextra -Wno-unused-parameter -g -O0
+CXXFLAGS := -std=c++17 -Wall -Wextra -Wno-unused-parameter -g -O0
 # Shim headers come FIRST so they override real headers
 INCLUDES := -Ishims -I. -I../9_1_1_C_Cpp_Libraries
 
+# C++ library directory (AGC, ADAR1000 Manager)
+CXX_LIB_DIR := ../9_1_1_C_Cpp_Libraries
+CXX_SRCS    := $(CXX_LIB_DIR)/ADAR1000_AGC.cpp $(CXX_LIB_DIR)/ADAR1000_Manager.cpp
+CXX_OBJS    := ADAR1000_AGC.o ADAR1000_Manager.o
+
 # Real source files compiled against mock headers
 REAL_SRC := ../9_1_1_C_Cpp_Libraries/adf4382a_manager.c
 
@@ -62,7 +69,10 @@ TESTS_STANDALONE := test_bug12_pa_cal_loop_inverted \
 # Tests that need platform_noos_stm32.o + mocks
 TESTS_WITH_PLATFORM := test_bug11_platform_spi_transmit_only
 
-ALL_TESTS := $(TESTS_WITH_REAL) $(TESTS_MOCK_ONLY) $(TESTS_STANDALONE) $(TESTS_WITH_PLATFORM)
+# C++ tests (AGC outer loop)
+TESTS_WITH_CXX := test_agc_outer_loop
+
+ALL_TESTS := $(TESTS_WITH_REAL) $(TESTS_MOCK_ONLY) $(TESTS_STANDALONE) $(TESTS_WITH_PLATFORM) $(TESTS_WITH_CXX)
 
 .PHONY: all build test clean \
         $(addprefix test_,bug1 bug2 bug3 bug4 bug5 bug6 bug7 bug8 bug9 bug10 bug11 bug12 bug13 bug14 bug15) \
@@ -156,6 +166,24 @@ test_gap3_emergency_state_ordering: test_gap3_emergency_state_ordering.c
 $(TESTS_WITH_PLATFORM): %: %.c $(MOCK_OBJS) $(PLATFORM_OBJ)
 	$(CC) $(CFLAGS) $(INCLUDES) $< $(MOCK_OBJS) $(PLATFORM_OBJ) -o $@
 
+# --- C++ object rules ---
+
+ADAR1000_AGC.o: $(CXX_LIB_DIR)/ADAR1000_AGC.cpp $(CXX_LIB_DIR)/ADAR1000_AGC.h
+	$(CXX) $(CXXFLAGS) $(INCLUDES) -c $< -o $@
+
+ADAR1000_Manager.o: $(CXX_LIB_DIR)/ADAR1000_Manager.cpp $(CXX_LIB_DIR)/ADAR1000_Manager.h
+	$(CXX) $(CXXFLAGS) $(INCLUDES) -c $< -o $@
+
+# --- C++ test binary rules ---
+
+test_agc_outer_loop: test_agc_outer_loop.cpp $(CXX_OBJS) $(MOCK_OBJS)
+	$(CXX) $(CXXFLAGS) $(INCLUDES) $< $(CXX_OBJS) $(MOCK_OBJS) -o $@
+
+# Convenience target
+.PHONY: test_agc
+test_agc: test_agc_outer_loop
+	./test_agc_outer_loop
+
 # --- Individual test targets ---
 
 test_bug1: test_bug1_timed_sync_init_ordering