fix(gui): align radar parameters to FPGA truth (radar_scene.py)

- Bandwidth 500 MHz -> 20 MHz, sample rate 4 MHz -> 100 MHz (DDC output)
- Range formula: deramped FMCW -> matched-filter c/(2*Fs)*decimation
- Velocity formula: use PRI (167 us) and chirps_per_subframe (16)
- Carrier frequency: 10.525 GHz -> 10.5 GHz per radar_scene.py
- Range per bin: 4.8 m -> 24 m, max range: 307 m -> 1536 m
- Fix simulator target spawn range to match new coverage (50-1400 m)
- Remove dead BANDWIDTH constant, add SAMPLE_RATE to V65 Tk
- All 174 tests pass, ruff clean

9_Firmware/9_3_GUI/v7/map_widget.py

@@ -98,7 +98,7 @@ class RadarMapWidget(QWidget):
         )
         self._targets: list[RadarTarget] = []
         self._pending_targets: list[RadarTarget] | None = None
-        self._coverage_radius = 50_000   # metres
+        self._coverage_radius = 1_536   # metres (64 bins x ~24 m/bin)
         self._tile_server = TileServer.OPENSTREETMAP
         self._show_coverage = True
         self._show_trails = False