feat: install nodes and the backend from a static compose file; remove dead code [CI]

Agent, Probe and Backend now start from one static compose.yaml plus a local
.env: the panel (or the release assets, for the very first Backend) provides
the file, the panel's command writes the public values into .env, checks the
file's SHA-256 and runs compose up. Updating is compose pull && compose up -d.
The image is chosen by the CI channel (:latest, or MOSHIRO_VERSION in .env),
not by the panel; the previous one-line script stays as a fallback.

- packaging/compose/{agent,probe,backend}/compose.yaml are the single source,
  embedded in the Backend and served at /install/compose/{file}; the root
  compose.yaml moved there. Releases also carry them and list them in the
  signed SHA256SUMS.
- The container entrypoint defaults the node name to the host name.
- Join token creation returns a compose block (.env, url, hash, per-platform
  commands); the admin dialog leads with it.
- Remove code with no references (HotLayer members, LiveHub.SubscriberCount,
  QueryService.ParseParams, ReleaseService.Forget, a few constants) and reduce
  the install-code lookup to the role it is for.

packaging/container/entrypoint.sh

@@ -1,5 +1,5 @@
 #!/bin/sh
-# 容器入口（Agent 和 Probe 共用）：第一次启动用 MOSHIRO_SERVER / MOSHIRO_JOIN / MOSHIRO_NAME 自己注册并写配置，
+# 容器入口（Agent 和 Probe 共用）：第一次启动用 MOSHIRO_SERVER / MOSHIRO_JOIN（MOSHIRO_NAME 不写就用主机名）自己注册并写配置，
 # 身份和配置都在命名卷 /etc/moshiro 里，之后重启（或换新镜像重建容器）直接启动，不需要再给参数。
 set -eu
 
@@ -9,8 +9,10 @@ identity="$dir/$role-id"
 config="$dir/$role.json"
 
 if [ ! -f "$identity/node.json" ]; then
-  if [ -z "${MOSHIRO_SERVER:-}" ] || [ -z "${MOSHIRO_JOIN:-}" ] || [ -z "${MOSHIRO_NAME:-}" ]; then
-    echo "first start: set MOSHIRO_SERVER, MOSHIRO_JOIN and MOSHIRO_NAME (the panel shows the complete command)" >&2
+  # 节点名字不写就用主机名（宿主网络下容器的主机名就是宿主机的）
+  MOSHIRO_NAME="${MOSHIRO_NAME:-$(hostname -s 2>/dev/null || hostname 2>/dev/null || echo node)}"
+  if [ -z "${MOSHIRO_SERVER:-}" ] || [ -z "${MOSHIRO_JOIN:-}" ]; then
+    echo "first start: set MOSHIRO_SERVER and MOSHIRO_JOIN in .env (the panel shows the complete content)" >&2
     exit 1
   fi
   # 每个节点都必须有属主（passkey）：信任根指纹和属主缺一个就不注册