fix: 9 bugs from code review — RTL sign-ext & snapshot, thread safety, protocol fixes

- rx_gain_control.v: sign-extension fix ({agc_gain[3],agc_gain} not {1'b0,agc_gain})
  + inclusive frame_boundary snapshot via combinational helpers (Bug #7)
- v7/dashboard.py: Qt thread-safe logging via pyqtSignal bridge (Bug #1)
  + table headers corrected to 'Range (m)' / 'Velocity (m/s)' (Bug #2)
- main.cpp: guard outerAgc.applyGain() with if(outerAgc.enabled) (Bug #3)
- radar_protocol.py: replay L1 threshold detection when CFAR disabled (Bug #4)
  + IndexError guard in replay open (Bug #5) + AGC opcodes in _HARDWARE_ONLY_OPCODES
- radar_dashboard.py: AGC monitor attribute name fixes (3 labels)
- tb_rx_gain_control.v: Tests 17-19 (sign-ext, simultaneous valid+boundary, enable toggle)
- tb_cross_layer_ft2232h.v: AGC opcode vectors 0x28-0x2C in Exercise A (Bug #6)

Vivado 50T build verified: WNS=+0.002ns, WHS=+0.028ns — all timing constraints met.
All tests pass: MCU 21/21, GUI 120/120, cross-layer 29/29, FPGA 25/25 (68 checks).

9_Firmware/9_3_GUI/v7/dashboard.py

@@ -36,7 +36,7 @@ from PyQt6.QtWidgets import (
     QTableWidget, QTableWidgetItem, QHeaderView,
     QPlainTextEdit, QStatusBar, QMessageBox,
 )
-from PyQt6.QtCore import Qt, QTimer, pyqtSlot
+from PyQt6.QtCore import Qt, QTimer, pyqtSignal, pyqtSlot, QObject
 
 from matplotlib.backends.backend_qtagg import FigureCanvasQTAgg
 from matplotlib.figure import Figure
@@ -173,8 +173,10 @@ class RadarDashboard(QMainWindow):
         self._gui_timer.timeout.connect(self._refresh_gui)
         self._gui_timer.start(100)
 
-        # Log handler for diagnostics
-        self._log_handler = _QtLogHandler(self._log_append)
+        # Log handler for diagnostics (thread-safe via Qt signal)
+        self._log_bridge = _LogSignalBridge(self)
+        self._log_bridge.log_message.connect(self._log_append)
+        self._log_handler = _QtLogHandler(self._log_bridge)
         self._log_handler.setLevel(logging.INFO)
         logging.getLogger().addHandler(self._log_handler)
 
@@ -403,7 +405,7 @@ class RadarDashboard(QMainWindow):
         self._targets_table_main = QTableWidget()
         self._targets_table_main.setColumnCount(5)
         self._targets_table_main.setHorizontalHeaderLabels([
-            "Range Bin", "Doppler Bin", "Magnitude", "SNR (dB)", "Track ID",
+            "Range (m)", "Velocity (m/s)", "Magnitude", "SNR (dB)", "Track ID",
         ])
         self._targets_table_main.setAlternatingRowColors(True)
         self._targets_table_main.setSelectionBehavior(
@@ -1719,15 +1721,22 @@ class RadarDashboard(QMainWindow):
 
 
 # =============================================================================
-# Qt-compatible log handler (routes Python logging -> QTextEdit)
+# Qt-compatible log handler (routes Python logging -> QTextEdit via signal)
 # =============================================================================
 
-class _QtLogHandler(logging.Handler):
-    """Sends log records to a callback (called on the thread that emitted)."""
 
-    def __init__(self, callback):
+class _LogSignalBridge(QObject):
+    """Thread-safe bridge: emits a Qt signal so the slot runs on the GUI thread."""
+
+    log_message = pyqtSignal(str)
+
+
+class _QtLogHandler(logging.Handler):
+    """Sends log records to a QObject signal (safe from any thread)."""
+
+    def __init__(self, bridge: _LogSignalBridge):
         super().__init__()
-        self._callback = callback
+        self._bridge = bridge
         self.setFormatter(logging.Formatter(
             "%(asctime)s  %(levelname)-8s  %(message)s",
             datefmt="%H:%M:%S",
@@ -1736,6 +1745,6 @@ class _QtLogHandler(logging.Handler):
     def emit(self, record):
         try:
             msg = self.format(record)
-            self._callback(msg)
+            self._bridge.log_message.emit(msg)
         except RuntimeError:
             pass