Fix review bugs: PD-sep counter leaks, hardcoded paths, missing deps

Critical:
- cache_aware_proxy: _handle_pd_sep leaked p_inst.num_requests (never
  decremented) and never managed d_inst.num_requests; fix media_type
  from application/json to text/event-stream for SSE stream

High:
- b3_sweep/b3_isolated_policy/b3_analyze: replace hardcoded
  /home/admin/cpfs/wjh/ ROOT with script-relative $(dirname "$0")/..
- b3_analyze: replace hardcoded 8-port WORKER_MAP with dynamic
  generation from BASE_PORT and N_INSTANCES

Medium:
- analyze_breakdown: warn on stderr when records are skipped (was silent)
- deploy_vllm_patches: fail-fast on SSH/SCP errors instead of
  continuing with empty VENV_SITE
- pyproject.toml: declare fastapi and uvicorn as runtime dependencies
- launch_elastic_p2p: kill EngineCore and proxy in trap handler to
  prevent GPU memory leaks on exit

scripts/launch_elastic_p2p.sh

@@ -27,7 +27,7 @@ PROXY_PORT=9090
 HEAVY_THRESHOLD="${HEAVY_THRESHOLD:-20000}"
 MAX_OFFLOAD="${MAX_OFFLOAD:-4}"
 
-trap 'echo "Cleaning up..."; kill $(jobs -p) 2>/dev/null; wait 2>/dev/null' EXIT INT TERM
+trap 'echo "Cleaning up..."; kill $(jobs -p) 2>/dev/null; pkill -9 -f "vllm serve" 2>/dev/null; pkill -9 -f "EngineCore" 2>/dev/null; pkill -9 -f cache_aware_proxy 2>/dev/null; wait 2>/dev/null' EXIT INT TERM
 
 echo "=== Elastic P2P Offload (${N_INSTANCES}× TP=1 kv_both) ==="
 echo "  Model:           $MODEL"