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).

2 files changed, 33 insertions, 1 deletions

diff --git a/src/zencore/include/zencore/fmtutils.h b/src/zencore/include/zencore/fmtutils.h
index a263c6f04..f062c4147 100644
--- a/src/zencore/include/zencore/fmtutils.h
+++ b/src/zencore/include/zencore/fmtutils.h
@@ -90,7 +90,7 @@ struct fmt::formatter<std::filesystem::path> : formatter<string_view>
 		using namespace std::literals;
 
 		zen::ExtendableStringBuilder<128> String;
-		String << Path.u8string();
+		zen::PathToUtf8(Path, String);
 		std::string_view PathView = String.ToView();
 
 		if (PathView.starts_with("\\\\?\\"sv))
diff --git a/src/zencore/include/zencore/intmath.h b/src/zencore/include/zencore/intmath.h
index 2b59d6f4a..b9f31d57b 100644
--- a/src/zencore/include/zencore/intmath.h
+++ b/src/zencore/include/zencore/intmath.h
@@ -38,6 +38,7 @@
 #if ZEN_COMPILER_MSC || ZEN_PLATFORM_WINDOWS
 #	pragma intrinsic(_BitScanReverse)
 #	pragma intrinsic(_BitScanReverse64)
+#	pragma intrinsic(_umul128)
 #else
 inline uint8_t
 _BitScanReverse(unsigned long* Index, uint32_t Mask)
@@ -205,6 +206,37 @@ Max(auto x, auto y)
 
 //////////////////////////////////////////////////////////////////////////
 
+// Precomputed reciprocal for fast 64-bit unsigned division by a constant.
+// Given divisor d, stores multiplier m and shift s such that
+// x / d == MulHi64(x, m) >> s for all x in the expected range.
+//
+// Uses the "round-up" method: m = ceil(2^(64+s) / d). The extra shift
+// parameter s is bumped when d is a power of two (where ceil would
+// overflow). For small divisors s == 0 always suffices.
+struct ReciprocalU64
+{
+	uint64_t Mul   = 0;
+	uint32_t Shift = 0;
+
+	ReciprocalU64() = default;
+	explicit ReciprocalU64(uint64_t Divisor);
+
+	uint32_t Divide(uint64_t Value) const
+	{
+		if (Mul == 0)
+		{
+			return uint32_t(Value);	 // Divisor <= 1
+		}
+#if ZEN_PLATFORM_WINDOWS
+		uint64_t Hi;
+		_umul128(Value, Mul, &Hi);
+#else
+		uint64_t Hi = uint64_t(((unsigned __int128)Value * Mul) >> 64);
+#endif
+		return uint32_t(Hi >> Shift);
+	}
+};
+
 void intmath_forcelink();  // internal
 
 }  // namespace zen