fix(launcher): detach stdin on agent container run (#5)

pi print mode reads piped stdin until EOF; an attached terminal stdin
blocked the one-shot run forever. Automated contexts (closed stdin)
never exposed it. Request text comes from the compose command.

Proven: tail -f /dev/null | scripts/hello.sh now returns MOSAIC_HELLO_OK
in ~4s (previously timed out at 30s); verify.sh remains green.

Closes #5

scripts/verify.sh

@@ -31,8 +31,9 @@ if ! docker image inspect "$IMAGE" >/dev/null 2>&1; then
 fi
 
 # 2. Run the agent request (stdout only = model response).
+# stdin detached: see hello.sh — print mode would block on a terminal.
 set +e
-RESPONSE="$(docker compose run --rm -T mosaic-agent 2>/tmp/mosaic-poc-stderr.$$)"
+RESPONSE="$(docker compose run --rm -T mosaic-agent </dev/null 2>/tmp/mosaic-poc-stderr.$$)"
 RC=$?
 set -e
 STDERR_FILE="/tmp/mosaic-poc-stderr.$$"