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.

backend/shared/MoShiro.Protocol/ProtocolLimits.cs

@@ -3,7 +3,6 @@ namespace MoShiro.Protocol;
 public static class ProtocolVersion
 {
     public const int Container = 1;
-    public const int Wire = 1;
 }
 
 public static class ProtocolLimits
@@ -39,5 +38,4 @@ public static class MoShiroCapabilities
 {
     public const string Base = "moshiro.v1";
     public const string KindsPrefix = "moshiro.kinds:";
-    public const string BlocksPrefix = "moshiro.blocks:";
 }