Dashboard overhaul, compute integration (#814)

- **Frontend dashboard overhaul**: Unified compute/main dashboards into a single shared UI. Added new pages for cache, projects, metrics, sessions, info (build/runtime config, system stats). Added live-update via WebSockets with pause control, sortable detail tables, themed styling. Refactored compute/hub/orchestrator pages into modular JS.
- **HTTP server fixes and stats**: Fixed http.sys local-only fallback when default port is in use, implemented root endpoint redirect for http.sys, fixed Linux/Mac port reuse. Added /stats endpoint exposing HTTP server metrics (bytes transferred, request rates). Added WebSocket stats tracking.
- **OTEL/diagnostics hardening**: Improved OTLP HTTP exporter with better error handling and resilience. Extended diagnostics services configuration.
- **Session management**: Added new sessions service with HTTP endpoints for registering, updating, querying, and removing sessions. Includes session log file support. This is still WIP.
- **CLI subcommand support**: Added support for commands with subcommands in the zen CLI tool, with improved command dispatch.
- **Misc**: Exposed CPU usage/hostname to frontend, fixed JS compact binary float32/float64 decoding, limited projects displayed on front page to 25 sorted by last access, added vscode:// link support.

Also contains some fixes from TSAN analysis.

1 files changed, 78 insertions, 0 deletions

diff --git a/src/zen/zen.cpp b/src/zen/zen.cpp
index 7f7afa322..9a466da2e 100644
--- a/src/zen/zen.cpp
+++ b/src/zen/zen.cpp
@@ -194,6 +194,84 @@ ZenCmdBase::GetSubCommand(cxxopts::Options&,
 	return argc;
 }
 
+ZenSubCmdBase::ZenSubCmdBase(std::string_view Name, std::string_view Description)
+: m_SubOptions(std::string(Name), std::string(Description))
+{
+	m_SubOptions.add_options()("h,help", "Print help");
+}
+
+void
+ZenCmdWithSubCommands::AddSubCommand(ZenSubCmdBase& SubCmd)
+{
+	m_SubCommands.push_back(&SubCmd);
+}
+
+bool
+ZenCmdWithSubCommands::OnParentOptionsParsed(const ZenCliOptions& /*GlobalOptions*/)
+{
+	return true;
+}
+
+void
+ZenCmdWithSubCommands::Run(const ZenCliOptions& GlobalOptions, int argc, char** argv)
+{
+	std::vector<cxxopts::Options*> SubOptionPtrs;
+	SubOptionPtrs.reserve(m_SubCommands.size());
+	for (ZenSubCmdBase* SubCmd : m_SubCommands)
+	{
+		SubOptionPtrs.push_back(&SubCmd->SubOptions());
+	}
+
+	cxxopts::Options*  MatchedSubOption = nullptr;
+	std::vector<char*> SubCommandArguments;
+	int				   ParentArgc = GetSubCommand(Options(), argc, argv, SubOptionPtrs, MatchedSubOption, SubCommandArguments);
+
+	if (!ParseOptions(Options(), ParentArgc, argv))
+	{
+		return;
+	}
+
+	if (MatchedSubOption == nullptr)
+	{
+		ExtendableStringBuilder<128> VerbList;
+		for (bool First = true; ZenSubCmdBase * SubCmd : m_SubCommands)
+		{
+			if (!First)
+			{
+				VerbList.Append(", ");
+			}
+			VerbList.Append(SubCmd->SubOptions().program());
+			First = false;
+		}
+		throw OptionParseException(fmt::format("No subcommand specified. Available subcommands: {}", VerbList.ToView()), Options().help());
+	}
+
+	ZenSubCmdBase* MatchedSubCmd = nullptr;
+	for (ZenSubCmdBase* SubCmd : m_SubCommands)
+	{
+		if (&SubCmd->SubOptions() == MatchedSubOption)
+		{
+			MatchedSubCmd = SubCmd;
+			break;
+		}
+	}
+	ZEN_ASSERT(MatchedSubCmd != nullptr);
+
+	// Parse subcommand args before OnParentOptionsParsed so --help on the subcommand
+	// works without requiring parent options like --hosturl to be populated.
+	if (!ParseOptions(*MatchedSubOption, gsl::narrow<int>(SubCommandArguments.size()), SubCommandArguments.data()))
+	{
+		return;
+	}
+
+	if (!OnParentOptionsParsed(GlobalOptions))
+	{
+		return;
+	}
+
+	MatchedSubCmd->Run(GlobalOptions);
+}
+
 static ReturnCode
 GetReturnCodeFromHttpResult(const HttpClientError& Ex)
 {