tools/cubec: fix CLI so ./check stress works; separate client flags from command

cubec forwarded its OWN leading options (--socket/--tenant/...) verbatim
into the command payload sent to the daemon, so 'cubec --socket SOCK
"prog ..."' made the server reject '--socket' as an unknown command.
stress.sh therefore produced 'error: unknown command: --socket' on every
sample and measured nothing.

Split cubec arg parsing into client-option vs command-payload so flags are
consumed locally and only the command reaches the daemon. The canonical
'./check stress' stage now drives a real daemon and samples stats.

tools/stress.sh

@@ -47,6 +47,9 @@ PAIRS=0
 SAMPLE_EVERY=25          # sample stats every 25 pairs (~ once a second at load)
 while [ "$(date +%s)" -lt "$END" ]; do
   X=$((PAIRS % 256))
+  # Flags MUST precede the command: `cubec` parses --socket/--tenant as leading
+  # options, so `"$CLI" --socket SOCK "prog ..."` would turn the trailing
+  # --socket into an unknown subcommand. Pass flags first.
   "$CLI" --socket "$SOCK" "prog /c077/z001/y001/x$X const $((PAIRS % 97)) halt" >/dev/null 2>&1
   "$CLI" --socket "$SOCK" "run  /c077/z001/y001/x$X"                    >/dev/null 2>&1
   PAIRS=$((PAIRS + 1))