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/deploy_vllm_patches.sh

@@ -29,11 +29,18 @@ if [ "$HOST" = "local" ]; then
     done
 else
     # Find site-packages on remote
-    VENV_SITE=$(ssh "$HOST" "~/agentic-kv/.venv/bin/python -c \"import site; print(site.getsitepackages()[0])\"")
+    VENV_SITE=$(ssh "$HOST" "~/agentic-kv/.venv/bin/python -c \"import site; print(site.getsitepackages()[0])\"") || {
+        echo "ERROR: failed to resolve site-packages on $HOST" >&2; exit 1;
+    }
+    if [ -z "$VENV_SITE" ]; then
+        echo "ERROR: empty site-packages path from $HOST" >&2; exit 1;
+    fi
     DST="$VENV_SITE/vllm"
     echo "Deploying to $HOST:$DST"
     for f in "${PATCHED_FILES[@]}"; do
-        scp "$VLLM_SRC/$f" "$HOST:$DST/$f"
+        scp "$VLLM_SRC/$f" "$HOST:$DST/$f" || {
+            echo "ERROR: failed to copy $f to $HOST" >&2; exit 1;
+        }
     done
 fi