feat(tb): add independent KG/EN/DE testbenches

- sync_rtl/kg/TB/tb_kg_xsim.v + xsim_run.tcl
- sync_rtl/en/TB/tb_en_xsim.v + xsim_run.tcl
- sync_rtl/de/TB/tb_de_xsim.v + xsim_run.tcl

Run individual tests:
  ./run_tb.sh kg   (KeyGen only, ~47K cycles)
  ./run_tb.sh en   (Encaps only)
  ./run_tb.sh de   (Decaps only)

sync_rtl/en/TB/xsim_run.tcl

@@ -0,0 +1,132 @@
+# 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 Encaps-only testbench
+#
+# Compiles ALL RTL dependencies for mlkem_top plus the Encaps-only testbench.
+# Run from the project root: ~/Dev/mlkem/
+#
+# Prerequisites:
+#   source /opt/Xilinx/Vivado/2019.2/settings64.sh
+#
+# Usage:
+#   vivado -mode batch -source sync_rtl/en/TB/xsim_run.tcl
+
+# ================================================================
+# 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/en/TB
+
+# ================================================================
+# Step 1: Compile common infrastructure
+# ================================================================
+puts "=== Compiling common infrastructure ==="
+xvlog -sv -i . ${COMMON_DIR}/pipeline_reg.v
+xvlog -sv -i . ${COMMON_DIR}/skid_buffer.v
+
+# ================================================================
+# Step 2: Compile SHA3 / Keccak core
+# ================================================================
+puts "=== Compiling SHA3/Keccak core ==="
+xvlog -sv ${SHA3_DIR}/keccak_round.v
+xvlog -sv ${SHA3_DIR}/keccak_core.v
+xvlog -sv -i . ${SHA3_DIR}/sha3_top.v
+
+# ================================================================
+# Step 3: Compile SHA3 chain (G function)
+# ================================================================
+puts "=== Compiling SHA3 chain ==="
+xvlog -sv -i . ${SHA3C_DIR}/sha3_chain_top_shared.v
+
+# ================================================================
+# Step 4: Compile RNG
+# ================================================================
+puts "=== Compiling RNG ==="
+xvlog -sv ${RNG_DIR}/rng_sync.v
+
+# ================================================================
+# Step 5: Compile NTT core and dependencies
+# ================================================================
+puts "=== Compiling NTT core ==="
+xvlog -sv ${NTT_DIR}/zeta_rom.v
+xvlog -sv ${NTT_DIR}/barrett_mul.v
+xvlog -sv ${NTT_DIR}/butterfly_unit.v
+xvlog -sv -i . ${NTT_DIR}/ntt_core.v
+
+# ================================================================
+# Step 6: Compile polynomial arithmetic
+# ================================================================
+puts "=== Compiling polynomial arithmetic ==="
+xvlog -sv ${PA_DIR}/poly_arith_sync.v
+
+# ================================================================
+# Step 7: Compile polynomial multiplication
+# ================================================================
+puts "=== Compiling polynomial multiplication ==="
+xvlog -sv ${PM_DIR}/poly_mul_zeta_rom.v
+xvlog -sv ${PM_DIR}/basecase_mul.v
+xvlog -sv -i . ${PM_DIR}/poly_mul_sync.v
+
+# ================================================================
+# Step 8: Compile sampling modules
+# ================================================================
+puts "=== Compiling sampling modules ==="
+xvlog -sv -i . ${CBD_DIR}/sample_cbd_sync_shared.v
+xvlog -sv -i . ${SNT_DIR}/sample_ntt_sync_shared.v
+
+# ================================================================
+# Step 9: Compile compression and modular arithmetic
+# ================================================================
+puts "=== Compiling compression and modular arithmetic ==="
+xvlog -sv ${CD_DIR}/comp_decomp_sync.v
+xvlog -sv ${MA_DIR}/mod_add_sync.v
+
+# ================================================================
+# Step 10: Compile storage (BRAM)
+# ================================================================
+puts "=== Compiling storage BRAMs ==="
+xvlog -sv ${STOR_DIR}/s_bram.v
+xvlog -sv ${STOR_DIR}/sd_bram.v
+
+# ================================================================
+# Step 11: Compile top-level integration
+# ================================================================
+puts "=== Compiling top-level integration ==="
+xvlog -sv -i . ${TOP_DIR}/keccak_arbiter.v
+xvlog -sv -i . ${TOP_DIR}/mlkem_top.v
+
+# ================================================================
+# Step 12: Compile testbench
+# ================================================================
+puts "=== Compiling Encaps-only testbench ==="
+xvlog -sv ${TB_DIR}/tb_en_xsim.v
+
+# ================================================================
+# Step 13: Elaborate snapshot (xelab)
+# ================================================================
+puts "=== Elaborating snapshot ==="
+xelab tb_en_xsim -s tb_en_xsim --timescale 1ns/1ps
+
+# ================================================================
+# Step 14: Run simulation
+# ================================================================
+puts ""
+puts "=== Running Encaps-only simulation ==="
+xsim tb_en_xsim -R
+
+puts ""
+puts "=== Encaps simulation complete ==="