harden error_strings[] safety and update .gitignore

- Add ERROR_COUNT sentinel to SystemError_t enum
- Change error_strings[] to static const char* const
- Add static_assert to enforce enum/array sync at compile time
- Add runtime bounds check with fallback for invalid error codes
- Add all missing test binary names to .gitignore

9_Firmware/9_1_Microcontroller/tests/.gitignore

@@ -3,18 +3,38 @@
 *.dSYM/
 
 # Test binaries (built by Makefile)
+# TESTS_WITH_REAL
 test_bug1_timed_sync_init_ordering
-test_bug2_ad9523_double_setup
 test_bug3_timed_sync_noop
 test_bug4_phase_shift_before_check
 test_bug5_fine_phase_gpio_only
+test_bug9_platform_ops_null
+test_bug10_spi_cs_not_toggled
+test_bug15_htim3_dangling_extern
+
+# TESTS_MOCK_ONLY
+test_bug2_ad9523_double_setup
 test_bug6_timer_variable_collision
 test_bug7_gpio_pin_conflict
 test_bug8_uart_commented_out
-test_bug9_platform_ops_null
-test_bug10_spi_cs_not_toggled
-test_bug11_platform_spi_transmit_only
+test_bug14_diag_section_args
+test_gap3_emergency_stop_rails
+
+# TESTS_STANDALONE
 test_bug12_pa_cal_loop_inverted
 test_bug13_dac2_adc_buffer_mismatch
-test_bug14_diag_section_args
-test_bug15_htim3_dangling_extern
+test_gap3_iwdg_config
+test_gap3_temperature_max
+test_gap3_idq_periodic_reread
+test_gap3_emergency_state_ordering
+test_gap3_overtemp_emergency_stop
+test_gap3_health_watchdog_cold_start
+
+# TESTS_WITH_PLATFORM
+test_bug11_platform_spi_transmit_only
+
+# TESTS_WITH_CXX
+test_agc_outer_loop
+
+# Manual / one-off test builds
+test_um982_gps