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/MoShiro.Backend.Api.csproj

@@ -10,6 +10,9 @@
     <EmbeddedResource Include="..\..\..\packaging\install\install.sh" LogicalName="install.sh" />
     <EmbeddedResource Include="..\..\..\packaging\install\install.ps1" LogicalName="install.ps1" />
     <EmbeddedResource Include="..\..\..\packaging\update\release-key.pub.pem" LogicalName="release-key.pub.pem" />
+    <EmbeddedResource Include="..\..\..\packaging\compose\agent\compose.yaml" LogicalName="compose-agent.yaml" />
+    <EmbeddedResource Include="..\..\..\packaging\compose\probe\compose.yaml" LogicalName="compose-probe.yaml" />
+    <EmbeddedResource Include="..\..\..\packaging\compose\backend\compose.yaml" LogicalName="compose-backend.yaml" />
   </ItemGroup>
   <!-- 前端构建产物（web 目录下 npm run build）内嵌进 Backend；没构建时不嵌入，Backend 只提供 API -->
   <ItemGroup Condition="Exists('..\..\..\web\display\dist\index.html')">