Move the route proxy into its module and run it from the trust image, on mesh-sdk's public membership (issues 1633, 1634, 1635)

A bundle is built only from its module's directory (ADR 0480 clause 4), so the proxy leaves
examples/ and the controller's internal/broker; the broker keeps no second copy of what the
proxy shares with mesh-sdk. The image and its Dockerfile go, and a test holds that only
build-agent declares one (clause 11).

Makefile

@@ -90,15 +90,6 @@ redis-provisioner-image:
 	@echo
 	@docker image inspect $(REDIS_PROVISIONER_IMAGE) --format 'built {{.RepoTags}}  {{.Size}} bytes'
 
-# The proxy that turns a route grant into traffic reaching a workload.
-PROXY_IMAGE ?= mesh-route-proxy:$(VERSION)
-PROXY_DEV_TAG ?= mesh-route-proxy:development
-
-proxy-image:
-	docker build --build-arg GO_BASE=$(GO_BASE) -f modules/route-proxy/Dockerfile -t $(PROXY_IMAGE) -t $(PROXY_DEV_TAG) .
-	@echo
-	@docker image inspect $(PROXY_IMAGE) --format 'built {{.RepoTags}}  {{.Size}} bytes'
-
 # The whole check. Raises a database, runs the repository's own check against it -- merge-check.sh,
 # the very script `mesh/repo-check` runs -- and takes the database down again, including when the
 # check fails, which is why the teardown is not conditional and the script's exit status is the