feat: 2048-pt FFT upgrade with decimation=4, 512 output bins, 6m spacing

Complete cross-layer upgrade from 1024-pt/64-bin to 2048-pt/512-bin FFT:

FPGA RTL (14+ modules):
- radar_params.vh: FFT_SIZE=2048, RANGE_BINS=512, 9-bit range, 6-bit stream
- fft_engine.v: 2048-pt FFT with XPM BRAM
- chirp_memory_loader_param.v: 2 segments x 2048 (was 4 x 1024)
- matched_filter_multi_segment.v: BRAM inference for overlap_cache, explicit ov_waddr
- mti_canceller.v: BRAM inference for prev_i/q arrays (was fabric FFs)
- doppler_processor.v: 16384-deep memory, 14-bit addressing
- cfar_ca.v: 512 rows, indentation fix
- radar_receiver_final.v: rising-edge detector for frame_complete, 11-bit sample_addr
- range_bin_decimator.v: 512 output bins
- usb_data_interface_ft2232h.v: bulk per-frame with Manhattan magnitude
- radar_mode_controller.v: XOR edge detector for toggle signals
- rx_gain_control.v: updated for new bin count

Python GUI + Protocol (8 files):
- radar_protocol.py: 512-bin bulk frame parser, LSB-first bitmap
- GUI_V65_Tk.py, v7/*.py: updated for 512 bins, 6m range resolution

Golden data + tests:
- All .hex/.csv/.npy golden references regenerated for 2048/512
- fft_twiddle_2048.mem added
- Deleted stale seg2/seg3 chirp mem files
- 9 new bulk frame cross-layer tests, deleted 6 stale per-sample tests
- Deleted stale tb_cross_layer_ft2232h.v and dead contract_parser functions
- Updated validate_mem_files.py for 2048/2-segment config

MCU: RadarSettings.cpp max_distance/map_size 1536->3072

All 4 CI jobs pass: 285 tests, 0 failures, 0 skips

9_Firmware/9_3_GUI/v7/dashboard.py

@@ -72,7 +72,7 @@ if TYPE_CHECKING:
 logger = logging.getLogger(__name__)
 
 # Frame dimensions from FPGA
-NUM_RANGE_BINS = 64
+NUM_RANGE_BINS = 512
 NUM_DOPPLER_BINS = 32
 
 # Force C locale (period as decimal separator) for all QDoubleSpinBox instances.
@@ -92,7 +92,7 @@ def _make_dspin() -> QDoubleSpinBox:
 # =============================================================================
 
 class RangeDopplerCanvas(FigureCanvasQTAgg):
-    """Matplotlib canvas showing the 64x32 Range-Doppler map with dark theme."""
+    """Matplotlib canvas showing the 512x32 Range-Doppler map with dark theme."""
 
     def __init__(self, _parent=None):
         fig = Figure(figsize=(10, 6), facecolor=DARK_BG)
@@ -104,7 +104,7 @@ class RangeDopplerCanvas(FigureCanvasQTAgg):
             extent=[0, NUM_DOPPLER_BINS, 0, NUM_RANGE_BINS], origin="lower",
         )
 
-        self.ax.set_title("Range-Doppler Map (64x32)", color=DARK_FG)
+        self.ax.set_title("Range-Doppler Map (512x32)", color=DARK_FG)
         self.ax.set_xlabel("Doppler Bin", color=DARK_FG)
         self.ax.set_ylabel("Range Bin", color=DARK_FG)
         self.ax.tick_params(colors=DARK_FG)
@@ -643,9 +643,9 @@ class RadarDashboard(QMainWindow):
         btn_trigger.clicked.connect(lambda: self._send_fpga_cmd(0x02, 1))
         op_layout.addWidget(btn_trigger)
 
-        # Stream Control (3-bit mask)
-        self._add_fpga_param_row(op_layout, "Stream Control", 0x04, 7, 3,
-                                 "0-7, 3-bit mask, rst=7")
+        # Stream Control (6-bit)
+        self._add_fpga_param_row(op_layout, "Stream Control", 0x04, 63, 6,
+                                 "0-63, 6-bit stream/format, rst=15")
 
         btn_status = QPushButton("Request Status")
         btn_status.clicked.connect(lambda: self._send_fpga_cmd(0xFF, 0))
@@ -1639,7 +1639,7 @@ class RadarDashboard(QMainWindow):
 
     @pyqtSlot(object)
     def _on_frame_ready(self, frame: RadarFrame):
-        """Handle a complete 64x32 radar frame from production acquisition."""
+        """Handle a complete 512x32 radar frame from production acquisition."""
         self._current_frame = frame
         self._frame_count += 1