Add internal ACME CA (step-ca) as a generic acme-ca provision; wire route-proxy to consume it

Piece C of ADR 0056: an internal authority certifies routed names by the same
path a public one would, with the proxy pointed at whichever issuer the mesh
names and trusting that issuer's root.

step-ca (new): provides acme-ca (mesh scope), listens 9000 from mesh, persists
its CA home under uid 1000. The root CA cert reaches consumers as a served
value settled from a per-mesh operator setting (no baked root); the init
password and root key are sealed secrets, not literals. No route-name -> IP
hosts map (that is Piece B). Upstream smallstep/step-ca pinned by Docker Hub
digest.

route-proxy: requires + binds acme-ca. ACME_DIRECTORY is composed on the
consumer side from ${bound:acme-ca:at}:${bound:acme-ca:port}, and ACME_CA_BUNDLE
is a file whose content is ${bound:acme-ca:root} -- both from the binding,
replacing the hardcoded directory and the baked root PEM.

Claude-Session: https://claude.ai/code/session_01LrgweAeERJYBg88c5cKDzF

modules/route-proxy/module.json

@@ -16,6 +16,12 @@
   "receives": {
     "route": "/var/lib/route-proxy/routes/mesh.json"
   },
+  "requires": [
+    "acme-ca"
+  ],
+  "binds": {
+    "acme-ca": "/var/lib/route-proxy/acme-ca.json"
+  },
   "listens": [
     {
       "port": 80,
@@ -49,22 +55,46 @@
       "path": "/var/lib/route-proxy/acme",
       "mode": "0700"
     },
+    {
+      "id": "ca-dir",
+      "type": "directory",
+      "path": "/var/lib/route-proxy/ca",
+      "mode": "0755"
+    },
+    {
+      "id": "ca-bundle",
+      "type": "file",
+      "path": "/var/lib/route-proxy/ca/root.crt",
+      "mode": "0644",
+      "content": "${bound:acme-ca:root}\n"
+    },
+    {
+      "id": "acme-env",
+      "type": "file",
+      "path": "/var/lib/route-proxy/acme.env",
+      "mode": "0600",
+      "content": "ACME_DIRECTORY=https://${bound:acme-ca:at}:${bound:acme-ca:port}/acme/acme/directory\n"
+    },
     {
       "id": "server",
       "type": "container",
       "name": "route-proxy",
       "image": "mesh-route-proxy@sha256:0000000000000000000000000000000000000000000000000000000000000000",
       "network": "host",
+      "env-file": [
+        "/var/lib/route-proxy/acme.env"
+      ],
       "volumes": [
         "/var/lib/route-proxy/routes:/routes:ro",
-        "/var/lib/route-proxy/acme:/acme"
+        "/var/lib/route-proxy/acme:/acme",
+        "/var/lib/route-proxy/ca:/ca:ro"
       ],
       "env": {
         "ROUTES": "/routes/mesh.json",
         "LISTEN": ":80",
         "TLS_LISTEN": ":443",
         "ACME_CACHE": "/acme",
-        "ACME_DIRECTORY": "https://acme-staging-v02.api.letsencrypt.org/directory"
+        "ACME_CA_BUNDLE": "/ca/root.crt"
       }
     }
   ]

modules/step-ca/module.json

@@ -0,0 +1,79 @@
+{
+  "module": "step-ca",
+  "version": "1",
+  "capabilities": [
+    "container-runtime"
+  ],
+  "provides": [
+    {
+      "name": "acme-ca",
+      "scope": "mesh"
+    }
+  ],
+  "serves": {
+    "acme-ca": {}
+  },
+  "listens": [
+    {
+      "port": 9000,
+      "protocol": "tcp",
+      "from": "mesh",
+      "why": "the ACME directory and step-ca API; a proxy on any node reaches it here over the mesh to obtain certificates, and its single listen is what the consumer is told the port is"
+    }
+  ],
+  "own-secrets": {
+    "password": "/var/lib/mesh/step-ca/password",
+    "root-key": "/var/lib/mesh/step-ca/root-key"
+  },
+  "resources": [
+    {
+      "id": "mesh-state",
+      "type": "directory",
+      "path": "/var/lib/mesh/step-ca",
+      "mode": "0700"
+    },
+    {
+      "id": "home",
+      "type": "directory",
+      "path": "/var/lib/step-ca",
+      "mode": "0700",
+      "owner": "1000:1000"
+    },
+    {
+      "id": "config",
+      "type": "file",
+      "path": "/var/lib/mesh/step-ca/config.json",
+      "mode": "0644",
+      "content": "{}",
+      "merge": "json"
+    },
+    {
+      "id": "init-env",
+      "type": "file",
+      "path": "/var/lib/mesh/step-ca/init.env",
+      "mode": "0600",
+      "content": "DOCKER_STEPCA_INIT_PASSWORD=${secret:password}\n"
+    },
+    {
+      "id": "server",
+      "type": "container",
+      "name": "step-ca",
+      "image": "smallstep/step-ca@sha256:a2b17872915c193259b75a5474c398326f41bd199f0842093e52cf4182bc8270",
+      "network": "host",
+      "env-file": [
+        "/var/lib/mesh/step-ca/init.env"
+      ],
+      "env": {
+        "DOCKER_STEPCA_INIT_NAME": "Mesh Internal CA",
+        "DOCKER_STEPCA_INIT_DNS_NAMES": "localhost,127.0.0.1",
+        "DOCKER_STEPCA_INIT_ACME": "true",
+        "DOCKER_STEPCA_INIT_REMOTE_MANAGEMENT": "false"
+      },
+      "volumes": [
+        "/var/lib/step-ca:/home/step",
+        "/var/lib/mesh/step-ca/root-key:/run/secrets/root-key:ro",
+        "/var/lib/mesh/step-ca/config.json:/run/config/config.json:ro"
+      ]
+    }
+  ]
+}