feat(serve): set APEX I-Compact as default, harden benchmark workflow

Serving:
- make serve now launches Claude-distilled APEX 35B-A3B (16GB) with 2
  parallel slots and 256K context as the daily driver
- add serve-custom for ad-hoc model testing
- add flush-gpu to reclaim unified memory after stuck runs

Benchmarks:
- default Vulkan-only backends (ROCm trails at long context)
- add --backends filter to run-baseline.sh
- fix backend filter substring bug (grep -qFx for exact line match)
- fix model filter regex metacharacter bug (grep -qiF for literal)
- respect --tg in long-context tests instead of hardcoded n=32

ROCm bump to 7.2.1 (kernel 6.18.4+ patch); keep 7.2 as optional.

Catalog:
- add mudler APEX I-Compact (Claude-distilled 35B, 17GB)
- add 0xSero REAP-40 (pruned 122B-A10B, 46GB)
- update download instructions: hf download (huggingface-cli is gone)

scripts/benchmark/setup.sh

@@ -15,8 +15,8 @@ log_header "Benchmark Setup"
 # ── 1. Check toolbox containers ──────────────────────────
 log_info "Checking toolbox containers..."
 
-REQUIRED_TOOLBOXES=("llama-vulkan-radv" "llama-rocm-7.2")
-OPTIONAL_TOOLBOXES=("llama-rocm-6.4.4" "llama-vulkan-amdvlk")
+REQUIRED_TOOLBOXES=("llama-vulkan-radv" "llama-rocm-7.2.1")
+OPTIONAL_TOOLBOXES=("llama-rocm-7.2" "llama-rocm-6.4.4" "llama-vulkan-amdvlk")
 
 existing=$(detect_toolbox_names 2>/dev/null || true)
 missing=()