feat(tb): add KAT testbench for mlkem_top (ML-KEM-512)

- gen_vectors.py: parse kat_MLKEM_512.rsp, generate hex vectors
- tb_mlkem_top_xsim.v: force-inject d/msg/z for KAT testing
- mlkem_top_input.hex: 5 vectors (d + msg + z)
- mlkem_top_expected.hex: 5 vectors (pk + sk + ct + ss)
- xsim_run.tcl: full dependency chain compilation

Known issue: mlkem_top FSM has combinational race on rng_valid_i
- rng_valid_i driven by state_r (registered) causes rng_sync
  to miss valid_i pulse when state transitions at posedge
- Fix: change rng_valid_i to use state_next pattern
  (same as sha3_top uses state_next for kc_valid_i)

sync_rtl/top/TB/xsim_run.tcl

@@ -0,0 +1,187 @@
+# NOTE: On some systems, you may need:
+#   export LD_PRELOAD=/usr/lib64/libtinfo.so.5
+# before running this script.
+
+# xsim_run.tcl - Vivado xsim compilation and simulation for mlkem_top KAT testbench
+#
+# Compiles ALL RTL dependencies for mlkem_top plus the testbench.
+# Run from the project root: ~/Dev/mlkem/
+#
+# Prerequisites:
+#   source /opt/Xilinx/Vivado/2019.2/settings64.sh
+#
+# Usage examples:
+#   # Run mlkem_top KAT testbench
+#   xsim tb_mlkem_top_xsim -R
+#
+#   # Step-by-step:
+#   vivado -mode batch -source sync_rtl/top/TB/xsim_run.tcl
+#
+#   # Or via run_tb.sh:
+#   ./run_tb.sh mlkem_top
+
+# ================================================================
+# Configuration
+# ================================================================
+set COMMON_DIR   sync_rtl/common
+set SHA3_DIR     sync_rtl/sha3
+set SHA3C_DIR    sync_rtl/sha3_chain
+set RNG_DIR      sync_rtl/rng
+set NTT_DIR      sync_rtl/ntt
+set PA_DIR       sync_rtl/poly_arith
+set PM_DIR       sync_rtl/poly_mul
+set CBD_DIR      sync_rtl/sample_cbd
+set SNT_DIR      sync_rtl/sample_ntt
+set CD_DIR       sync_rtl/comp_decomp
+set MA_DIR       sync_rtl/mod_add
+set STOR_DIR     sync_rtl/storage
+set TOP_DIR      sync_rtl/top
+set TB_DIR       sync_rtl/top/TB
+
+# ================================================================
+# Step 1: Compile common infrastructure
+# ================================================================
+puts "=== Compiling common infrastructure ==="
+
+# Pipeline register (used by many modules)
+xvlog -sv -i . ${COMMON_DIR}/pipeline_reg.v
+
+# Skid buffer (backpressure buffer)
+xvlog -sv -i . ${COMMON_DIR}/skid_buffer.v
+
+# ================================================================
+# Step 2: Compile SHA3 / Keccak core
+# ================================================================
+puts "=== Compiling SHA3/Keccak core ==="
+
+# Keccak round (combinational, θ/ρ/π/χ/ι)
+xvlog -sv ${SHA3_DIR}/keccak_round.v
+
+# Keccak core (24-round sequential keccak-f[1600])
+xvlog -sv ${SHA3_DIR}/keccak_core.v
+
+# SHA3 top wrapper (G/H/J modes, with internal keccak_core)
+xvlog -sv -i . ${SHA3_DIR}/sha3_top.v
+
+# ================================================================
+# Step 3: Compile SHA3 chain (G function)
+# ================================================================
+puts "=== Compiling SHA3 chain ==="
+
+# sha3_chain_top_shared (G: d → rho, sigma, with external keccak_core)
+xvlog -sv -i . ${SHA3C_DIR}/sha3_chain_top_shared.v
+
+# ================================================================
+# Step 4: Compile RNG
+# ================================================================
+puts "=== Compiling RNG ==="
+
+# rng_sync (256-bit Galois LFSR)
+xvlog -sv ${RNG_DIR}/rng_sync.v
+
+# ================================================================
+# Step 5: Compile NTT core and dependencies
+# ================================================================
+puts "=== Compiling NTT core ==="
+
+# Zeta ROM (twiddle factors, 128 × 12-bit)
+xvlog -sv ${NTT_DIR}/zeta_rom.v
+
+# Barrett modular multiplier (a·b mod q)
+xvlog -sv ${NTT_DIR}/barrett_mul.v
+
+# Butterfly unit (CT/GS butterfly for NTT/INTT)
+xvlog -sv ${NTT_DIR}/butterfly_unit.v
+
+# NTT core (256-coeff NTT/INTT FSM)
+xvlog -sv -i . ${NTT_DIR}/ntt_core.v
+
+# ================================================================
+# Step 6: Compile polynomial arithmetic
+# ================================================================
+puts "=== Compiling polynomial arithmetic ==="
+
+# poly_arith_sync (element-wise poly add/sub)
+xvlog -sv ${PA_DIR}/poly_arith_sync.v
+
+# ================================================================
+# Step 7: Compile polynomial multiplication
+# ================================================================
+puts "=== Compiling polynomial multiplication ==="
+
+# Zeta ROM for poly_mul (degree-1 basecase)
+xvlog -sv ${PM_DIR}/poly_mul_zeta_rom.v
+
+# Basecase multiplier (degree-1 Karatsuba)
+xvlog -sv ${PM_DIR}/basecase_mul.v
+
+# poly_mul_sync (NTT-domain polynomial multiplier)
+xvlog -sv -i . ${PM_DIR}/poly_mul_sync.v
+
+# ================================================================
+# Step 8: Compile sampling modules
+# ================================================================
+puts "=== Compiling sampling modules ==="
+
+# sample_cbd_sync_shared (CBD sampling with external keccak)
+xvlog -sv -i . ${CBD_DIR}/sample_cbd_sync_shared.v
+
+# sample_ntt_sync_shared (SampleNTT with external keccak)
+xvlog -sv -i . ${SNT_DIR}/sample_ntt_sync_shared.v
+
+# ================================================================
+# Step 9: Compile compression and modular arithmetic
+# ================================================================
+puts "=== Compiling compression and modular arithmetic ==="
+
+# comp_decomp_sync (Compress_q / Decompress_q)
+xvlog -sv ${CD_DIR}/comp_decomp_sync.v
+
+# mod_add_sync ((a + b) mod q, streaming)
+xvlog -sv ${MA_DIR}/mod_add_sync.v
+
+# ================================================================
+# Step 10: Compile storage (BRAM)
+# ================================================================
+puts "=== Compiling storage BRAMs ==="
+
+# Single-port BRAM
+xvlog -sv ${STOR_DIR}/s_bram.v
+
+# Simple dual-port BRAM
+xvlog -sv ${STOR_DIR}/sd_bram.v
+
+# ================================================================
+# Step 11: Compile top-level integration
+# ================================================================
+puts "=== Compiling top-level integration ==="
+
+# keccak_arbiter (round-robin arbiter for shared keccak)
+xvlog -sv -i . ${TOP_DIR}/keccak_arbiter.v
+
+# mlkem_top (top-level KeyGen/Encaps/Decaps FSM)
+xvlog -sv -i . ${TOP_DIR}/mlkem_top.v
+
+# ================================================================
+# Step 12: Compile testbench
+# ================================================================
+puts "=== Compiling testbench ==="
+
+# tb_mlkem_top_xsim (KAT vector testbench)
+xvlog -sv ${TB_DIR}/tb_mlkem_top_xsim.v
+
+# ================================================================
+# Step 13: Elaborate snapshot (xelab)
+# ================================================================
+puts "=== Elaborating snapshot ==="
+xelab tb_mlkem_top_xsim -s tb_mlkem_top_xsim --timescale 1ns/1ps
+
+# ================================================================
+# Step 14: Run simulation
+# ================================================================
+puts ""
+puts "=== Running mlkem_top KAT simulation ==="
+xsim tb_mlkem_top_xsim -R
+
+puts ""
+puts "=== mlkem_top simulation complete ==="