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, 3 insertions, 36 deletions

diff --git a/src/zen/cmds/ui_cmd.cpp b/src/zen/cmds/ui_cmd.cpp
index 28ab6c45c..3d3021857 100644
--- a/src/zen/cmds/ui_cmd.cpp
+++ b/src/zen/cmds/ui_cmd.cpp
@@ -2,6 +2,8 @@
 
 #include "ui_cmd.h"
 
+#include "browser_launcher.h"
+
 #include <zencore/except_fmt.h>
 #include <zencore/fmtutils.h>
 #include <zencore/logging.h>
@@ -9,11 +11,6 @@
 #include <zenutil/consoletui.h>
 #include <zenutil/zenserverprocess.h>
 
-#if ZEN_PLATFORM_WINDOWS
-#	include <zencore/windows.h>
-#	include <shellapi.h>
-#endif
-
 namespace zen {
 
 namespace {
@@ -83,40 +80,10 @@ UiCommand::OpenBrowser(std::string_view HostName)
 		}
 	}
 
-	bool Success = false;
-
 	ExtendableStringBuilder<256> FullUrl;
 	FullUrl << HostName << m_DashboardPath;
 
-#if ZEN_PLATFORM_WINDOWS
-	HINSTANCE Result = ShellExecuteA(nullptr, "open", FullUrl.c_str(), nullptr, nullptr, SW_SHOWNORMAL);
-	Success			 = reinterpret_cast<intptr_t>(Result) > 32;
-#else
-	// Validate URL doesn't contain shell metacharacters that could lead to command injection
-	std::string_view		   FullUrlView	  = FullUrl;
-	constexpr std::string_view DangerousChars = ";|&$`\\\"'<>(){}[]!#*?~\n\r";
-	if (FullUrlView.find_first_of(DangerousChars) != std::string_view::npos)
-	{
-		throw OptionParseException(fmt::format("URL contains invalid characters: '{}'", FullUrl), m_Options.help());
-	}
-
-#	if ZEN_PLATFORM_MAC
-	std::string Command = fmt::format("open \"{}\"", FullUrl);
-#	elif ZEN_PLATFORM_LINUX
-	std::string Command = fmt::format("xdg-open \"{}\"", FullUrl);
-#	else
-	ZEN_NOT_IMPLEMENTED("Browser launching not implemented on this platform");
-#	endif
-
-	Success = system(Command.c_str()) == 0;
-#endif
-
-	if (!Success)
-	{
-		throw zen::runtime_error("Failed to launch browser for '{}'", FullUrl);
-	}
-
-	ZEN_CONSOLE("Web browser launched for '{}' successfully", FullUrl);
+	LaunchBrowser(std::string_view(FullUrl));
 }
 
 void