tools: add llama.cpp comparison baseline + standard benchmark suite

Vendor llama.cpp as a submodule pinned to b9371 and add a one-click
benchmark driver that compares xserv against it on identical workloads:

- setup-llama-cpp.sh: network-optional CUDA build (SM120); convert-to-gguf.sh
  converts the same safetensors to BF16 GGUF for an apples-to-apples baseline.
- tools/bench/: black-box OpenAI-API driver measuring TTFT/TPOT/throughput
  (single-stream + concurrent) and response quality on AIME 2025 + GSM8K.
- fetch_datasets.py pulls datasets to local JSON (GPU host has no network);
  task loaders prefer the local JSON.
- sync-and-build.sh: `bench` subcommand transfers source + datasets to the
  GPU host via tar-over-ssh (no rsync there), builds, and runs the suite.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tools/convert-to-gguf.sh

@@ -0,0 +1,55 @@
+#!/usr/bin/env bash
+# Convert a HuggingFace safetensors model dir into a BF16 GGUF for llama.cpp.
+#
+# Why BF16: we run xserv in BF16, so the baseline must run BF16 too. If we
+# compared xserv-BF16 against llama.cpp-Q4_K_M the speed delta would be
+# dominated by quantization, not by our kernels — that's not an apples-to-
+# apples comparison.
+#
+# Usage:
+#   tools/convert-to-gguf.sh <hf-model-dir> [out.gguf]
+#
+# Example:
+#   tools/convert-to-gguf.sh /opt/wjh/models/qwen3-8b
+#   # → /opt/wjh/models/qwen3-8b/qwen3-8b-bf16.gguf
+
+set -euo pipefail
+
+if [ "$#" -lt 1 ]; then
+    echo "Usage: $0 <hf-model-dir> [out.gguf]" >&2
+    exit 1
+fi
+
+SRC="$(realpath "$1")"
+ROOT_DIR="$(cd "$(dirname "$0")/.." && pwd)"
+CONVERT_PY="$ROOT_DIR/third_party/llama.cpp/convert_hf_to_gguf.py"
+
+if [ ! -f "$CONVERT_PY" ]; then
+    echo "convert script not found: $CONVERT_PY" >&2
+    echo "Run tools/setup-llama-cpp.sh first." >&2
+    exit 1
+fi
+
+if [ ! -d "$SRC" ]; then
+    echo "source model dir not found: $SRC" >&2
+    exit 1
+fi
+
+if [ "$#" -ge 2 ]; then
+    OUT="$2"
+else
+    BASENAME="$(basename "$SRC")"
+    OUT="$SRC/${BASENAME}-bf16.gguf"
+fi
+
+if [ -f "$OUT" ]; then
+    echo "==> already exists: $OUT (skipping; remove to force re-convert)"
+    echo "$OUT"
+    exit 0
+fi
+
+echo "==> converting $SRC -> $OUT (BF16)"
+python3 "$CONVERT_PY" "$SRC" --outfile "$OUT" --outtype bf16
+
+echo "=== done ==="
+echo "$OUT"