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.

backend/tests/MoShiro.Backend.Tests/InstallTests.cs

@@ -107,6 +107,9 @@ public sealed class InstallTests
         Assert.Contains("no-new-privileges:true", body, StringComparison.Ordinal);
         Assert.Contains("- ALL", body, StringComparison.Ordinal); // cap_drop
         Assert.DoesNotContain("jt_", body, StringComparison.Ordinal); // 没有任何一次性的值
+        // 参数只从 .env 原样传进容器：podman-compose 不替换环境变量里的默认值，写成 ${变量:-默认值} 会把字面量传给节点
+        Assert.Contains("env_file:", body, StringComparison.Ordinal);
+        Assert.DoesNotContain(":-}", body, StringComparison.Ordinal);
     }
 
     [Theory]