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, 16 insertions, 4 deletions

diff --git a/src/zenstore/cache/cachedisklayer.cpp b/src/zenstore/cache/cachedisklayer.cpp
index 45a4b6456..22b9d0be5 100644
--- a/src/zenstore/cache/cachedisklayer.cpp
+++ b/src/zenstore/cache/cachedisklayer.cpp
@@ -140,25 +140,37 @@ namespace cache::impl {
 	const char* LogExtension   = ".slog";
 	const char* MetaExtension  = ".meta";
 
+	std::filesystem::path GetBucketFilePath(const std::filesystem::path& BucketDir, const std::string& BucketName, const char* Extension)
+	{
+		ExtendablePathBuilder<256> Path;
+		Path.Append(BucketDir);
+		Path /= BucketName.c_str();
+		Path << Extension;
+		return Path.ToPath();
+	}
+
 	std::filesystem::path GetIndexPath(const std::filesystem::path& BucketDir, const std::string& BucketName)
 	{
-		return BucketDir / (BucketName + IndexExtension);
+		return GetBucketFilePath(BucketDir, BucketName, IndexExtension);
 	}
 
 	std::filesystem::path GetMetaPath(const std::filesystem::path& BucketDir, const std::string& BucketName)
 	{
-		return BucketDir / (BucketName + MetaExtension);
+		return GetBucketFilePath(BucketDir, BucketName, MetaExtension);
 	}
 
 	std::filesystem::path GetLogPath(const std::filesystem::path& BucketDir, const std::string& BucketName)
 	{
-		return BucketDir / (BucketName + LogExtension);
+		return GetBucketFilePath(BucketDir, BucketName, LogExtension);
 	}
 
 	std::filesystem::path GetManifestPath(const std::filesystem::path& BucketDir, const std::string& BucketName)
 	{
 		ZEN_UNUSED(BucketName);
-		return BucketDir / "zen_manifest";
+		ExtendablePathBuilder<256> Path;
+		Path.Append(BucketDir);
+		Path /= "zen_manifest";
+		return Path.ToPath();
 	}
 
 	bool ValidateCacheBucketIndexEntry(const DiskIndexEntry& Entry, std::string& OutReason)