Join: mesh-knowledge's page address is no word of the environment

The overview page read MESH_KNOWLEDGE_PAGE, which nothing in the mesh
sets; only its bus test did, to serve no page. checks/environment,
which came with A3's merge, refuses such a read. The page listens on
the port its manifest declares; the test's bundle sets the package's
address empty instead.

Claude-Session: https://claude.ai/code/session_01JG73KJNrH5EgFXMKKYSrig

modules/mesh-knowledge/cmd/mesh-knowledge/kit_test.go

@@ -38,6 +38,7 @@ func TestMain(m *testing.M) {
 		// The bundle the bus test starts: the knowledge base as the runtime launches it, its store in memory.
 		k := newKB(newMemStore())
 		k.Now = func() time.Time { return bundleDay }
+		pageAddress = ""
 		serve(k, os.Getenv("MESH_KNOWLEDGE_STATUS"))
 		os.Exit(0)
 	}