fix: compose passes .env through env_file; clearer name and channel messages [CI]

podman-compose does not substitute defaults inside "environment:" (a value
like ${MOSHIRO_NAME:-} reached the node as the literal text), so the node was
enrolled with an invalid name and reported the wrong network scope. The three
compose files now read .env with env_file and only interpolate image and
network_mode; the Backend .env keys are the container's own names
(MoShiro__PublicUrl, MoShiro__ClaimCode).

- The generated .env no longer carries a comment line for MOSHIRO_NAME; the
  dialog says how to choose a name instead.
- The container entrypoint prints the name it enrolls with and defaults
  MOSHIRO_NETWORK_SCOPE to host (Docker Desktop sets container in .env).
- The overview and line pages say "measurement channel not established"
  instead of "not connected": the agent can be reachable and pingable while
  the measurement TCP/UDP path is not.

web/admin/src/pages/JoinTokenCreated.tsx

@@ -30,7 +30,7 @@ export function JoinTokenCreated({ created, kind, onClose }: { created: CreatedJ
         <div className="notice warn">一次性码只显示这一次，请现在就复制。下面只有公开的值（面板地址、一次性码、信任根指纹和属主），没有任何私钥。</div>
         <Field
           label={`容器安装（推荐）：在要加入的机器上运行（${kind}）`}
-          hint="需要 podman compose 或 docker compose。命令建一个目录，把参数写进 .env（权限 600），下载 compose.yaml 并核对 SHA-256，一致才启动。节点名字默认取主机名，想自己定就改 .env 里的 MOSHIRO_NAME。"
+          hint="需要 podman compose 或 docker compose。命令建一个目录，把参数写进 .env（权限 600），下载 compose.yaml 并核对 SHA-256，一致才启动。节点名字默认取主机名；想自己定，在 .env 里加一行 MOSHIRO_NAME=名字（1–64 个字母、数字、点、下划线、横线）。"
         >
           <CommandTabs storageKey="moshiro.compose_tab" initial={initial} tabs={composeTabs} />
         </Field>