fix(tb): fix Vivado 2019.2 compatibility and add run_tb.sh

- Replace -include_dirs . with -i . (Vivado 2019.2 syntax)
- Add --timescale 1ns/1ps to all xelab commands
- Add LD_PRELOAD comment for ncurses compatibility
- Add run_tb.sh convenience script
  Usage: ./run_tb.sh mod_add
         ./run_tb.sh --list
- Update spec with Vivado 2019.2 compatibility notes

sync_rtl/rng/TB/xsim_run.tcl

@@ -1,3 +1,7 @@
+# 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 script for rng_sync
 #
 # Compiles rng_sync RTL plus the file-based vector testbench and runs simulation.
@@ -42,7 +46,7 @@ xvlog -sv ${TB_DIR}/tb_rng_xsim.v
 # ================================================================
 puts "=== Elaborating snapshot ==="
 
-xelab tb_rng_xsim -s tb_rng_xsim
+xelab tb_rng_xsim -s tb_rng_xsim --timescale 1ns/1ps
 
 # ================================================================
 # Step 4: Run simulation