Fix review P2s: lockfile, model path convention, trap robustness

- Regenerate uv.lock after adding fastapi/uvicorn deps so uv sync
  --locked no longer fails
- B3 scripts: default MODEL to $HOME/models/... matching documented
  convention and other launch scripts (repo has no models/ directory)
- launch_elastic_p2p: append || true to each trap command so set -e
  doesn't abort cleanup when jobs -p is empty and EngineCore orphans
  remain

scripts/b3_sweep.sh

@@ -16,7 +16,7 @@ set -euo pipefail
 
 ROOT="${ROOT:-$(cd "$(dirname "$0")/.." && pwd)}"
 VENV="$ROOT/.venv/bin"
-MODEL="${MODEL:-$ROOT/models/Qwen/Qwen3-Coder-30B-A3B-Instruct}"
+MODEL="${MODEL:-$HOME/models/Qwen/Qwen3-Coder-30B-A3B-Instruct}"
 TRACE="${TRACE:-$ROOT/traces/w600_r0.0015_st30.jsonl}"
 OUTDIR="${OUTDIR:-$ROOT/outputs/b3_sweep_$(date +%Y%m%d_%H%M%S)}"
 PROXY_PORT="${PROXY_PORT:-9300}"