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/src/MoShiro.Backend.Api/Admin/AgentEndpoints.cs

@@ -143,7 +143,7 @@ public static class AgentEndpoints
             return Problems.From(http, ownerError);
         }
 
-        var plan = new InstallPlan(genesis, controllers, InstallScripts.Sha256(InstallScripts.Sh), InstallScripts.Sha256(InstallScripts.Ps1));
+        var plan = new InstallPlan(genesis, controllers, InstallScripts.Sha256(InstallScripts.Sh), InstallScripts.Sha256(InstallScripts.Ps1), InstallScripts.ComposeSha256(request.Role ?? JoinTokenService.AgentRole));
         http.SetDetail($"{request.Role ?? JoinTokenService.AgentRole}: {request.Note}");
         Result<CreatedJoinToken> result = await tokens.CreateAsync(
             new Application.CreateJoinTokenRequest(request.Note, request.Labels, request.AutoApprove ?? true, request.MaxUses ?? 1, request.ExpiresInHours ?? 24, request.Role ?? JoinTokenService.AgentRole, http.GetPrincipal().Label), baseUrl, plan, http.RequestAborted);
@@ -154,7 +154,7 @@ public static class AgentEndpoints
 
         http.Response.Headers.CacheControl = "no-store";
         http.Response.Headers.Location = "/api/admin/join-tokens";
-        return TypedResults.Json(new CreatedJoinTokenDto(Mappers.ToDto(created.Info), created.Plaintext, new InstallCommandsDto(created.InstallCommands.Linux, created.InstallCommands.Macos, created.InstallCommands.Windows)), ApiJsonContext.Default.CreatedJoinTokenDto, statusCode: StatusCodes.Status201Created);
+        return TypedResults.Json(new CreatedJoinTokenDto(Mappers.ToDto(created.Info), created.Plaintext, new InstallCommandsDto(created.InstallCommands.Linux, created.InstallCommands.Macos, created.InstallCommands.Windows), new ComposeInstallDto(created.Compose.Env, created.Compose.Url, created.Compose.Sha256, created.Compose.Linux, created.Compose.Macos, created.Compose.Windows)), ApiJsonContext.Default.CreatedJoinTokenDto, statusCode: StatusCodes.Status201Created);
     }
 
     private static async Task<IResult> RevokeTokenAsync(JoinTokenService tokens, string id, bool? purge, CancellationToken ct)