chore(bench): build servers into .sx-tmp; fix stale example path

The bench built sx-server/zig-server into bench/ (committed as stray
artifacts) and pointed at the pre-migration examples/32-http-server.sx.
Now builds into the gitignored .sx-tmp/ and uses the current
examples/1602-platform-http-server.sx, so a run leaves the tree clean.

bench/run.sh

@@ -5,6 +5,9 @@
 set -e
 cd "$(dirname "$0")/.."
 
+# Build outputs go in the gitignored scratch dir, not the tree.
+mkdir -p .sx-tmp
+
 REQUESTS=${1:-10000}
 CONCURRENCY=${2:-50}
 WARMUP=500
@@ -31,11 +34,11 @@ echo ""
 
 # --- Build ---
 echo -e "${BOLD}Building sx server...${RESET}"
-time_sx_build=$( { time ./zig-out/bin/sx build examples/32-http-server.sx -o bench/sx-server 2>&1; } 2>&1 | tail -1 )
+time_sx_build=$( { time ./zig-out/bin/sx build examples/1602-platform-http-server.sx -o .sx-tmp/sx-server 2>&1; } 2>&1 | tail -1 )
 echo "  $time_sx_build"
 
 echo -e "${BOLD}Building zig server...${RESET}"
-time_zig_build=$( { time zig build-exe bench/http-server.zig -O ReleaseFast -femit-bin=bench/zig-server 2>&1; } 2>&1 | tail -1 )
+time_zig_build=$( { time zig build-exe bench/http-server.zig -O ReleaseFast -femit-bin=.sx-tmp/zig-server 2>&1; } 2>&1 | tail -1 )
 echo "  $time_zig_build"
 echo ""
 
@@ -68,7 +71,7 @@ run_bench() {
 }
 
 # --- sx server ---
-bench/sx-server > /dev/null 2>&1 &
+.sx-tmp/sx-server > /dev/null 2>&1 &
 SX_PID=$!
 wait_for_port $SX_PORT
 
@@ -79,7 +82,7 @@ SX_PID=""
 sleep 0.5
 
 # --- zig server ---
-bench/zig-server > /dev/null 2>&1 &
+.sx-tmp/zig-server > /dev/null 2>&1 &
 ZIG_PID=$!
 wait_for_port $ZIG_PORT