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

pyproject.toml

@@ -6,6 +6,8 @@ requires-python = ">=3.10"
 dependencies = [
     "httpx>=0.27",
     "numpy>=1.24",
+    "fastapi>=0.110",
+    "uvicorn>=0.29",
 ]
 
 [project.optional-dependencies]