fix(fpga): TX-G — surface chirps_mismatch_error to host status

`chirps_mismatch_error` was set in radar_system_top when the host
requested chirps_per_elev != Doppler FFT size, but never wired into the
USB status response — a latent silent failure.

Wired the flag through both USB interfaces (FT601 + FT2232H) into bit
[10] of status word 4 (was reserved). GUI parser exposes it as
StatusResponse.chirps_mismatch.

- usb_data_interface*.v: new status_chirps_mismatch input, packed at [10]
- radar_system_top.v: connect chirps_mismatch_error to both USB instances
- radar_protocol.py + test_GUI_V65_Tk.py: parse new bit, +1 round-trip test
- tb_usb_data_interface.v: drive the new port, update word-4 expectation

Tests: GUI 92/92 (was 91), MCU 75/75, USB TB 91/91, ruff clean repo-wide.
The 2 remaining FPGA regression failures (Receiver Integration, MF Chain)
are the pre-existing iverilog-can't-link-Xilinx-IP issue tracked
separately as the open RX-NEW-3 follow-up.

9_Firmware/9_3_GUI/radar_protocol.py

@@ -147,6 +147,7 @@ class StatusResponse:
     agc_peak_magnitude: int = 0  # 8-bit peak magnitude [7:0]
     agc_saturation_count: int = 0  # 8-bit saturation count [7:0]
     agc_enable: int = 0          # 1-bit AGC enable readback
+    chirps_mismatch: int = 0     # TX-G: 1 if FPGA clamped/rejected host chirps_per_elev
 
 
 # ============================================================================
@@ -247,9 +248,9 @@ class RadarProtocol:
         # Word 3: {short_listen[31:16], 10'd0, chirps_per_elev[5:0]}
         sr.chirps_per_elev = words[3] & 0x3F
         sr.short_listen = (words[3] >> 16) & 0xFFFF
-        # Word 4: {agc_current_gain[31:28], agc_peak_magnitude[27:20],
-        #          agc_saturation_count[19:12], agc_enable[11], 9'd0, range_mode[1:0]}
+        # Word 4 layout: gain[31:28] peak[27:20] sat[19:12] agc_en[11] mismatch[10] mode[1:0]
         sr.range_mode = words[4] & 0x03
+        sr.chirps_mismatch = (words[4] >> 10) & 0x01
         sr.agc_enable = (words[4] >> 11) & 0x01
         sr.agc_saturation_count = (words[4] >> 12) & 0xFF
         sr.agc_peak_magnitude = (words[4] >> 20) & 0xFF