fix(fpga): F-0.1 wire AD9484 OR overrange pin into diagnostics

The AD9484 OR (overrange) LVDS pair is routed on the 50T main board to
xc7a50t-ftg256 bank-14 pins M6/N6 but was previously left unconnected at
the top level. Plumb it through the full stack so saturation at the raw
ADC boundary shows up in the existing overflow aggregation:

- ad9484_interface_400m: add adc_or_p/n inputs, IBUFDS + IDDR capture of
  both phases in the BUFIO domain, re-register into the clk_400m BUFG
  domain, OR rise|fall into adc_overrange_400m output.
- radar_receiver_final: stickify adc_overrange_400m in clk_400m, CDC to
  clk_100m via a 2FF ASYNC_REG chain (same reasoning as F-1.2's
  cdc_cic_fir_overrun — single-bit, latched low→high, GPIO-class
  diagnostic), OR into the existing ddc_overflow_any aggregation.
- radar_system_top: expose adc_or_p/n top-level ports and pass through.
- xc7a50t_ftg256.xdc: anchor M6/N6 as LVDS_25 DIFF_TERM, with the same
  DCO-relative input-delay constraints as adc_d_p[*].
- xc7a200t_fbg484.xdc: IOSTANDARD/DIFF_TERM set; PACKAGE_PIN left as a
  documented TODO — the 200T dev-board schematic has not been checked
  and the 200T build will need the anchor filled in before place/route.

9_Firmware/9_2_FPGA/constraints/xc7a50t_ftg256.xdc

@@ -290,6 +290,22 @@ set_input_delay -clock [get_clocks adc_dco_p] -min 0.2 [get_ports {adc_d_p[*]}]
 set_input_delay -clock [get_clocks adc_dco_p] -max 1.0 -clock_fall [get_ports {adc_d_p[*]}] -add_delay
 set_input_delay -clock [get_clocks adc_dco_p] -min 0.2 -clock_fall [get_ports {adc_d_p[*]}] -add_delay
 
+# --------------------------------------------------------------------------
+# Audit F-0.1: AD9484 OR (overrange) LVDS pair (Bank 14)
+# Schematic RADAR_Main_Board.sch: ADC_OR_P → U42 IO_L19P_T3_A10_D26_14 (M6)
+#                                  ADC_OR_N → U42 IO_L19N_T3_A09_D25_VREF_14 (N6)
+# DDR-sourced by adc_dco_p, same timing class as adc_d_p[*].
+# --------------------------------------------------------------------------
+set_property PACKAGE_PIN M6 [get_ports {adc_or_p}]
+set_property PACKAGE_PIN N6 [get_ports {adc_or_n}]
+set_property IOSTANDARD LVDS_25 [get_ports {adc_or_p}]
+set_property IOSTANDARD LVDS_25 [get_ports {adc_or_n}]
+set_property DIFF_TERM TRUE [get_ports {adc_or_p}]
+set_input_delay -clock [get_clocks adc_dco_p] -max 1.0 [get_ports {adc_or_p}]
+set_input_delay -clock [get_clocks adc_dco_p] -min 0.2 [get_ports {adc_or_p}]
+set_input_delay -clock [get_clocks adc_dco_p] -max 1.0 -clock_fall [get_ports {adc_or_p}] -add_delay
+set_input_delay -clock [get_clocks adc_dco_p] -min 0.2 -clock_fall [get_ports {adc_or_p}] -add_delay
+
 # ============================================================================
 # FT2232H USB 2.0 INTERFACE (Bank 35, VCCO=3.3V)
 # ============================================================================