zen trace analysis support (#945)

Integrates the **tourist** trace analysis library and builds a full `zen trace` command suite for working with Unreal Engine `.utrace` files.

### Trace analysis library (`thirdparty/tourist/`)
- Adds the tourist library as a third-party dependency with three modules: **foundation** (platform primitives, memory, scheduling), **trace** (UE Trace protocol decoding), and **analysis** (event dispatching and analyzer framework).
- Cross-platform support for Windows, Linux, and macOS.

### `zen trace` CLI commands (`src/zen/cmds/`, `src/zen/trace/`)
- **`zen trace analyze`** — Summarize a `.utrace` file: session metadata, thread inventory, command line + build configuration, CPU profiling scopes, timing, event rates, log messages, and (with symbols) memory allocation metrics including live-allocs dumps, callstack-keyed aggregation, and allocation churn. Optional HTML output for memory reports.
- **`zen trace inspect`** — Dump the event schema (declared types, fields, sizes) from a trace file.
- **`zen trace trim`** — Extract a time-window from a trace into a new `.utrace` file.
- **`zen trace serve`** — Launch a local HTTP server hosting an interactive trace viewer; opens in the default browser.

### Symbolication (`src/zen/trace/symbol_resolver.*`, `thirdparty/raw_pdb/`)
- Pluggable resolver with multiple backends: `pdb` (in-tree raw_pdb), `dbghelp` (Windows), `llvm-symbolizer` (all platforms), `atos` (macOS). An `auto` backend picks the best available tool per platform.
- Microsoft Symbol Server support: downloads PDBs on demand using a redirect-aware HTTP client.
- Local PDB cache keyed by image GUID preserves symbols across binary recompilation.
- Callstack trimming heuristic strips UE internal noise from reports.
- Binary analysis cache (`.ucache_z`) avoids re-resolving the same trace.

### Interactive trace viewer (`src/zen/frontend/html/`, `src/zen/trace/trace_viewer_service.*`)
- Timeline: scope-level detail, horizontal zoom/pan, vertical scrolling, viewport-driven loading with pre-computed LOD for responsive navigation of large traces.
- Thread grouping (collapsible sidebar sections) synthesized from name suffixes, natural sort order, visual distinction between lane threads and OS threads.
- Bookmark and region annotations; region categories with per-category toggles; bookmark marker toggle in the toolbar.
- Filterable Logs tab showing captured `UE_LOG` output.
- Stats tab with per-scope aggregate statistics.
- Memory tab with interactive allocation analysis and an allocation size histogram.
- CsvProfiler event parsing and chart UI.

### Other in-branch supporting changes
- **Cross-platform browser launcher** (`browser_launcher.{h,cpp}`) used by `trace serve`.
- **`ReciprocalU64`** fast 64-bit integer division (zencore/intmath) for trace analyzers.
- **`parallelsort`** cross-platform parallel sort helper (zenutil).
- Frontend zip build rule so the viewer's HTML assets are bundled into `zen.exe`.
- `/Zo` flag for better optimized debug info on Windows release builds.
- `trace-tests.cpp` in the `zen-test` harness (harness itself landed on main via #985).

1 files changed, 71 insertions, 0 deletions

diff --git a/src/zen/browser_launcher.cpp b/src/zen/browser_launcher.cpp
new file mode 100644
index 000000000..a115bf46a
--- /dev/null
+++ b/src/zen/browser_launcher.cpp
@@ -0,0 +1,71 @@
+// Copyright Epic Games, Inc. All Rights Reserved.
+
+#include "browser_launcher.h"
+
+#include <zenbase/zenbase.h>
+#include <zencore/except_fmt.h>
+#include <zencore/logging.h>
+
+#include <stdexcept>
+#include <string>
+
+#if ZEN_PLATFORM_WINDOWS
+#	include <zencore/windows.h>
+#	include <shellapi.h>
+#else
+#	include <spawn.h>
+#	include <sys/wait.h>
+extern char** environ;
+#endif
+
+namespace zen {
+
+void
+LaunchBrowser(std::string_view Url)
+{
+	if (Url.empty())
+	{
+		throw zen::runtime_error("Cannot launch browser with empty URL");
+	}
+
+	bool Success = false;
+
+#if ZEN_PLATFORM_WINDOWS
+	std::string UrlZ(Url);
+	HINSTANCE	Result = ShellExecuteA(nullptr, "open", UrlZ.c_str(), nullptr, nullptr, SW_SHOWNORMAL);
+	Success			   = reinterpret_cast<intptr_t>(Result) > 32;
+#else
+#	if ZEN_PLATFORM_MAC
+	const char* Program = "open";
+#	elif ZEN_PLATFORM_LINUX
+	const char* Program = "xdg-open";
+#	else
+	ZEN_NOT_IMPLEMENTED("Browser launching not implemented on this platform");
+	const char* Program = nullptr;
+#	endif
+
+	// Spawn directly via posix_spawnp to avoid the shell entirely, so URL contents
+	// cannot be interpreted as shell syntax regardless of what characters they contain.
+	std::string Url_c(Url);
+	char* const Argv[]	= {const_cast<char*>(Program), Url_c.data(), nullptr};
+	pid_t		Pid		= 0;
+	const int	SpawnRc = posix_spawnp(&Pid, Program, nullptr, nullptr, Argv, environ);
+	if (SpawnRc == 0)
+	{
+		int Status = 0;
+		if (waitpid(Pid, &Status, 0) == Pid)
+		{
+			Success = WIFEXITED(Status) && WEXITSTATUS(Status) == 0;
+		}
+	}
+#endif
+
+	if (!Success)
+	{
+		throw zen::runtime_error("Failed to launch browser for '{}'", Url);
+	}
+
+	ZEN_CONSOLE("Web browser launched for '{}' successfully", Url);
+}
+
+}  // namespace zen