feat: hybrid AGC (FPGA phases 1-3 + GUI phase 6) with timing fix

FPGA:
- rx_gain_control.v rewritten: per-frame peak/saturation tracking,
  auto-shift AGC with attack/decay/holdoff, signed gain -7 to +7
- New registers 0x28-0x2C (agc_enable/target/attack/decay/holdoff)
- status_words[4] carries AGC metrics (gain, peak, sat_count, enable)
- DIG_5 GPIO outputs saturation flag for STM32 outer loop
- Both USB interfaces (FT601 + FT2232H) updated with AGC status ports

Timing fix (WNS +0.001ns -> +0.045ns, 45x improvement):
- CIC max_fanout 4->16 on valid pipeline registers
- +200ps setup uncertainty on 400MHz domain
- ExtraNetDelay_high placement + AggressiveExplore routing

GUI:
- AGC opcodes + status parsing in radar_protocol.py
- AGC control groups in both tkinter and V7 PyQt dashboards
- 11 new AGC tests (103/103 GUI tests pass)

Cross-layer:
- AGC opcodes/defaults/status assertions added (29/29 pass)
- contract_parser.py: fixed comment stripping in concat parser

All tests green: 25 FPGA + 103 GUI + 29 cross-layer = 157 pass

9_Firmware/9_2_FPGA/constraints/adc_clk_mmcm.xdc

@@ -83,3 +83,12 @@ set_false_path -through [get_pins rx_inst/adc/mmcm_inst/mmcm_adc_400m/LOCKED]
 # Waiving hold on these 8 paths (adc_d_p[0..7] → IDDR) is standard practice
 # for source-synchronous LVDS ADC interfaces using BUFIO capture.
 set_false_path -hold -from [get_ports {adc_d_p[*]}] -to [get_clocks adc_dco_p]
+
+# --------------------------------------------------------------------------
+# Timing margin for 400 MHz CIC critical path
+# --------------------------------------------------------------------------
+# The CIC decimator at 400 MHz has near-zero margin (WNS = +0.001 ns in
+# Build 26). Adding 200 ps of extra setup uncertainty forces Vivado to
+# leave comfortable margin for temperature/voltage/aging variation.
+# This is additive to the existing jitter-based uncertainty (~53 ps).
+set_clock_uncertainty -setup -add 0.200 [get_clocks clk_mmcm_out0]

9_Firmware/9_2_FPGA/constraints/xc7a50t_ftg256.xdc

@@ -222,8 +222,16 @@ set_property IOSTANDARD LVCMOS33 [get_ports {stm32_new_*}]
 set_property IOSTANDARD LVCMOS33 [get_ports {stm32_mixers_enable}]
 # reset_n is DIG_4 (PD12) — constrained above in the RESET section
 
-# DIG_5 = H11, DIG_6 = G12, DIG_7 = H12 — available for FPGA→STM32 status
-# Currently unused in RTL. Could be connected to status outputs if needed.
+# DIG_5 = H11, DIG_6 = G12, DIG_7 = H12 — FPGA→STM32 status outputs
+# DIG_5: AGC saturation flag (PD13 on STM32)
+# DIG_6: reserved (PD14)
+# DIG_7: reserved (PD15)
+set_property PACKAGE_PIN H11 [get_ports {gpio_dig5}]
+set_property PACKAGE_PIN G12 [get_ports {gpio_dig6}]
+set_property PACKAGE_PIN H12 [get_ports {gpio_dig7}]
+set_property IOSTANDARD LVCMOS33 [get_ports {gpio_dig*}]
+set_property DRIVE 8 [get_ports {gpio_dig*}]
+set_property SLEW SLOW [get_ports {gpio_dig*}]
 
 # ============================================================================
 # ADC INTERFACE (LVDS — Bank 14, VCCO=3.3V)