feat(gps): add UM982 GPS driver replacing broken TinyGPS++

Implement a complete UM982 GNSS driver (um982_gps.h/.c) with:
- NMEA parser for GGA, RMC, THS, VTG with multi-talker support (GP/GN/GL/GA/GB)
- Correct coordinate parsing using decimal-point-based degree detection
  (fixes PR #68 bug: 3-digit longitude degrees)
- Checksum verification on all incoming sentences
- Non-blocking line assembler with ring buffer
- Init sequence: UNLOG, HEADING FIXLENGTH, baseline config, NMEA enables,
  VERSIONA handshake (no SAVECONFIG to avoid NVM wear)
- Validity/age checks with configurable timeouts

Integration into main.cpp:
- Replace TinyGPSPlus with UM982_GPS_t, UART5 baud 9600->115200
- Non-blocking um982_process() in main loop (single-byte UART reads)
- GPS heading override with magnetometer fallback
- Health check using um982_position_age()

Test infrastructure:
- 49 unit tests covering checksums, coordinate parsing, all sentence types,
  talker IDs, feed/assembly, validity, init sequence, edge cases
- Mock HAL_UART_Receive with per-UART ring buffer for integration tests
- All 72 MCU tests passing (23 existing + 49 new)

Fixes all 12 bugs identified in PR #68 analysis (5 compile errors + 7 functional).

9_Firmware/9_1_Microcontroller/tests/Makefile

@@ -27,6 +27,10 @@ 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
 
+# GPS driver source
+GPS_SRC := ../9_1_3_C_Cpp_Code/um982_gps.c
+GPS_OBJ := um982_gps.o
+
 # Real source files compiled against mock headers
 REAL_SRC := ../9_1_1_C_Cpp_Libraries/adf4382a_manager.c
 
@@ -73,7 +77,10 @@ TESTS_WITH_PLATFORM := test_bug11_platform_spi_transmit_only
 # 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)
+# GPS driver tests (need mocks + GPS source + -lm)
+TESTS_GPS := test_um982_gps
+
+ALL_TESTS := $(TESTS_WITH_REAL) $(TESTS_MOCK_ONLY) $(TESTS_STANDALONE) $(TESTS_WITH_PLATFORM) $(TESTS_WITH_CXX) $(TESTS_GPS)
 
 .PHONY: all build test clean \
         $(addprefix test_,bug1 bug2 bug3 bug4 bug5 bug6 bug7 bug8 bug9 bug10 bug11 bug12 bug13 bug14 bug15) \
@@ -189,6 +196,20 @@ test_agc_outer_loop: test_agc_outer_loop.cpp $(CXX_OBJS) $(MOCK_OBJS)
 test_agc: test_agc_outer_loop
 	./test_agc_outer_loop
 
+# --- GPS driver rules ---
+
+$(GPS_OBJ): $(GPS_SRC)
+	$(CC) $(CFLAGS) $(INCLUDES) -I../9_1_3_C_Cpp_Code -c $< -o $@
+
+# Note: test includes um982_gps.c directly for white-box testing (static fn access)
+test_um982_gps: test_um982_gps.c $(MOCK_OBJS)
+	$(CC) $(CFLAGS) $(INCLUDES) -I../9_1_3_C_Cpp_Code $< $(MOCK_OBJS) -lm -o $@
+
+# Convenience target
+.PHONY: test_gps
+test_gps: test_um982_gps
+	./test_um982_gps
+
 # --- Individual test targets ---
 
 test_bug1: test_bug1_timed_sync_init_ordering