fix(fpga): implement 5 P0 invariant fixes with adversarial testbenches

Fixes 5 critical cross-layer invariant violations found during
system-level analysis. Each fix has a dedicated adversarial testbench
that actively tries to break the fix under race conditions, reset
mid-operation, overflow, and pathological input patterns.

RTL fixes:
- Fix #1: Replace flawed cdc_adc_to_processing with Gray-coded async
  FIFO (cdc_async_fifo) for DDC 400->100 MHz CDC path. Pre-fetch
  show-ahead architecture with CDC-safe registered reads.
- Fix #2: XOR toggle detection for mc_new_chirp in matched filter
  (cross-clock-domain safe vs level-sensitive).
- Fix #3: ST_WAIT_LISTEN state with configurable listen_delay to
  prevent matched filter re-trigger during chirp dead time.
- Fix #4: Overlap-save output trim in matched filter to suppress
  circular convolution artifacts at segment boundaries.
- Fix #7: Falling-edge frame_complete pulse in doppler_processor
  (was stuck high, causing continuous AGC resets).

RTL cleanup:
- Refactor CDC synchronizer arrays from memory arrays to scalar regs
  for explicit ASYNC_REG flop naming and synthesis constraint clarity.

Testbenches (70 checks total, all passing):
- tb_p0_async_fifo.v: 20 checks (fill, overflow, reset, streaming,
  show-ahead capacity, pathological data patterns)
- tb_p0_mf_adversarial.v: 33 checks (toggle detection, listen state,
  overlap trim, rapid chirp sequences, reset recovery)
- tb_p0_frame_pulse.v: 17 checks (pulse width, idle behavior,
  processing duration sweep, regression vs old stuck-high bug)

Regression: 24/24 pass (--quick), 57/57 existing CDC tests pass.
Golden references updated for doppler output timing change.

9_Firmware/9_2_FPGA/run_regression.sh

@@ -526,6 +526,25 @@ run_test "Radar Mode Controller" \
 
 echo ""
 
+# ===========================================================================
+# PHASE 5: P0 ADVERSARIAL TESTS — Invariant Violation Fixes
+# ===========================================================================
+echo "--- PHASE 5: P0 Adversarial Tests ---"
+
+run_test "P0 Fix #1: Async FIFO CDC (show-ahead, overflow, reset)" \
+    tb/tb_p0_async_fifo.vvp \
+    tb/tb_p0_async_fifo.v cdc_modules.v
+
+run_test "P0 Fixes #2/#3/#4: Matched Filter (toggle, listen, overlap)" \
+    tb/tb_p0_mf_adversarial.vvp \
+    tb/tb_p0_mf_adversarial.v matched_filter_multi_segment.v
+
+run_test "P0 Fix #7: Frame Complete Pulse (falling-edge)" \
+    tb/tb_p0_frame_pulse.vvp \
+    tb/tb_p0_frame_pulse.v
+
+echo ""
+
 # ===========================================================================
 # SUMMARY
 # ===========================================================================