feat(quic-interop): scaffold quic-interop-runner endpoint module

Adds :quic-interop, a JVM-only module at quic/interop/ that implements
the quic-interop-runner Docker contract so we can drive matrix tests
against aioquic / quiche / picoquic / msquic / ngtcp2 / etc. as a
bug-finding harness.

Phase 0 supports only the `handshake` testcase; everything else returns
127 so the runner skips rather than fails. SSLKEYLOGFILE / QLOGDIR
plumbing is deferred to Phase 1.

https://claude.ai/code/session_01HcvfQq1ttPV9PkRoJb4nyT

quic/interop/Makefile

@@ -0,0 +1,39 @@
+# Local iteration loop for the quic-interop-runner endpoint image.
+#
+#   make build              # compile JVM dist + build Docker image
+#   make smoke              # quick handshake test against a local picoquic
+#   make image-name         # print the image tag (for use in implementations.json)
+#
+# These targets are deliberately thin wrappers — the real harness is the
+# `quic-interop-runner` repo (clone separately and register `amethyst` with
+# image=amethyst-quic-interop:latest, role=client).
+IMAGE          ?= amethyst-quic-interop:latest
+REPO_ROOT      := $(shell git rev-parse --show-toplevel)
+DIST_DIR       := build/install/quic-interop
+PICOQUIC_PORT  ?= 4433
+
+.PHONY: build dist docker smoke image-name clean
+
+build: docker
+
+dist:
+	cd $(REPO_ROOT) && ./gradlew :quic-interop:installDist
+
+docker: dist
+	cd $(REPO_ROOT) && docker build -t $(IMAGE) -f quic/interop/Dockerfile .
+
+smoke: docker
+	@docker rm -f amethyst-quic-interop-smoke >/dev/null 2>&1 || true
+	docker run --rm --name amethyst-quic-interop-smoke \
+	    --network host \
+	    -e ROLE=client \
+	    -e TESTCASE=handshake \
+	    -e REQUESTS="https://127.0.0.1:$(PICOQUIC_PORT)/" \
+	    $(IMAGE)
+
+image-name:
+	@echo $(IMAGE)
+
+clean:
+	cd $(REPO_ROOT) && ./gradlew :quic-interop:clean
+	docker image rm -f $(IMAGE) 2>/dev/null || true