feat: node info, build info and acrylic web theme

Squash of recent dev work: return_session login, backend switcher, line
detail timeline, overview strips, node platform/country/ISP info with flags
and icons, build info (version, tag, time) behind site.show_build, and the
acrylic display theme.

backend/src/Monitor.Backend.Api/Contracts/ApiJsonContext.cs

@@ -37,6 +37,12 @@ namespace Monitor.Backend.Api;
 [JsonSerializable(typeof(AgentDto))]
 [JsonSerializable(typeof(PageDto<AgentDto>))]
 [JsonSerializable(typeof(AgentPatchRequest))]
+[JsonSerializable(typeof(BuildDto))]
+[JsonSerializable(typeof(AboutDto))]
+[JsonSerializable(typeof(NodeBuildDto))]
+[JsonSerializable(typeof(BuildInfoDto))]
+[JsonSerializable(typeof(NodeInfoDto))]
+[JsonSerializable(typeof(PageDto<NodeInfoDto>))]
 [JsonSerializable(typeof(JoinTokenDto))]
 [JsonSerializable(typeof(PageDto<JoinTokenDto>))]
 [JsonSerializable(typeof(CreateJoinTokenRequest))]