Wire self-test results (0x31) to USB status readback path, add fpga_self_test to regression

- usb_data_interface.v: Add 3 self-test status inputs, expand status packet
  from 7 words (header + 5 data + footer) to 8 words (header + 6 data + footer).
  New status_words[5] carries {busy, detail[7:0], flags[4:0]}.
- radar_system_top.v: Wire self_test_flags_latched, self_test_detail_latched,
  self_test_busy to usb_data_interface ports. Add opcode 0x31 as status
  readback alias so host can read self-test results.
- tb_usb_data_interface.v: Add self-test port connections, verify word 5 in
  Group 16, add Group 18 (busy flag + partial failure variant). 81 checks pass.
- run_regression.sh: Add fpga_self_test.v to PROD_RTL lint list and system-
  level compile lists. Add tb_fpga_self_test as Phase 1 unit test.
- 24/24 regression tests pass, lint clean (0 errors, 4 advisory warnings).

9_Firmware/9_2_FPGA/run_regression.sh

@@ -75,6 +75,7 @@ PROD_RTL=(
     rx_gain_control.v
     cfar_ca.v
     mti_canceller.v
+    fpga_self_test.v
 )
 
 # Source-only RTL (not instantiated at top level, but should still be lint-clean)
@@ -386,6 +387,10 @@ run_test "CFAR CA Detector" \
     tb/tb_cfar_ca.vvp \
     tb/tb_cfar_ca.v cfar_ca.v
 
+run_test "FPGA Self-Test" \
+    tb/tb_fpga_self_test.vvp \
+    tb/tb_fpga_self_test.v fpga_self_test.v
+
 echo ""
 
 # ===========================================================================
@@ -436,7 +441,7 @@ if [[ "$QUICK" -eq 0 ]]; then
         matched_filter_multi_segment.v matched_filter_processing_chain.v \
         range_bin_decimator.v doppler_processor.v xfft_32.v fft_engine.v \
         usb_data_interface.v edge_detector.v radar_mode_controller.v \
-        rx_gain_control.v cfar_ca.v mti_canceller.v
+        rx_gain_control.v cfar_ca.v mti_canceller.v fpga_self_test.v
 
     # E2E integration (46 strict checks: TX, RX, USB R/W, CDC, safety, reset)
     run_test "System E2E (tb_system_e2e)" \
@@ -450,7 +455,7 @@ if [[ "$QUICK" -eq 0 ]]; then
         matched_filter_multi_segment.v matched_filter_processing_chain.v \
         range_bin_decimator.v doppler_processor.v xfft_32.v fft_engine.v \
         usb_data_interface.v edge_detector.v radar_mode_controller.v \
-        rx_gain_control.v cfar_ca.v mti_canceller.v
+        rx_gain_control.v cfar_ca.v mti_canceller.v fpga_self_test.v
 else
     echo "  (skipped receiver golden + system top + E2E — use without --quick)"
     SKIP=$((SKIP + 4))