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/scripts/50t/build_50t.tcl

@@ -120,9 +120,10 @@ set_property CLOCK_DEDICATED_ROUTE FALSE [get_nets {ft_clkout_IBUF}]
 
 # ---- Run implementation steps ----
 opt_design -directive Explore
-place_design -directive Explore
+place_design -directive ExtraNetDelay_high
+phys_opt_design -directive AggressiveExplore
+route_design -directive AggressiveExplore
 phys_opt_design -directive AggressiveExplore
-route_design -directive Explore
 phys_opt_design -directive AggressiveExplore
 
 set impl_elapsed [expr {[clock seconds] - $impl_start}]