Transparent proxy mode (#823)

Adds a **transparent TCP proxy mode** to zenserver (activated via `zenserver proxy`), allowing it to sit between clients and upstream Zen servers to inspect and monitor HTTP/1.x traffic in real time. Primarily useful during development, to be able to observe multi-server/client interactions in one place.

- **Dedicated proxy port** -- Proxy mode defaults to port 8118 with its own data directory to avoid collisions with a normal zenserver instance.
- **TCP proxy core** (`src/zenserver/proxy/`) -- A new transparent TCP proxy that forwards connections to upstream targets, with support for both TCP/IP and Unix socket listeners. Multi-threaded I/O for connection handling. Supports Unix domain sockets for both upstream/downstream.
- **HTTP traffic inspection** -- Parses HTTP/1.x request/response streams inline to extract method, path, status, content length, and WebSocket upgrades without breaking the proxied data.
- **Proxy dashboard** -- A web UI showing live connection stats, per-target request counts, active connections, bytes transferred, and client IP/session ID rollups.
- **Server mode display** -- Dashboard banner now shows the running server mode (Zen Proxy, Zen Compute, etc.).

Supporting changes included in this branch:

- **Wildcard log level matching** -- Log levels can now be set per-category using wildcard patterns (e.g. `proxy.*=debug`).
- **`zen down --all`** -- New flag to shut down all running zenserver instances; also used by the new `xmake kill` task.
- Minor test stability fixes (flaky hash collisions, per-thread RNG seeds).
- Support ZEN_MALLOC environment variable for default allocator selection and switch default to rpmalloc
- Fixed sentry-native build to allow LTO on Windows

1 files changed, 9 insertions, 0 deletions

diff --git a/src/zenserver/main.cpp b/src/zenserver/main.cpp
index 09ecc48e5..26ae85ae1 100644
--- a/src/zenserver/main.cpp
+++ b/src/zenserver/main.cpp
@@ -31,6 +31,8 @@
 
 #include "hub/zenhubserver.h"
 
+#include "proxy/zenproxyserver.h"
+
 #if ZEN_PLATFORM_WINDOWS
 #	include <zencore/windows.h>
 #	include <zenutil/windows/windowsservice.h>
@@ -291,6 +293,7 @@ main(int argc, char* argv[])
 		kHub,
 		kStore,
 		kCompute,
+		kProxy,
 		kTest
 	} ServerMode = kStore;
 
@@ -308,6 +311,10 @@ main(int argc, char* argv[])
 		{
 			ServerMode = kCompute;
 		}
+		else if (argv[1] == "proxy"sv)
+		{
+			ServerMode = kProxy;
+		}
 		else if (argv[1] == "test"sv)
 		{
 			ServerMode = kTest;
@@ -333,6 +340,8 @@ main(int argc, char* argv[])
 			fprintf(stderr, "compute services are not compiled in!\n");
 			exit(5);
 #endif
+		case kProxy:
+			return AppMain<ZenProxyServerMain>(argc, argv);
 		default:
 		case kStore:
 			return AppMain<ZenStorageServerMain>(argc, argv);