Paper section: PD-sep scaffold + drop --enforce-eager from launch scripts

Adds analysis/pd_sep_paper_section/ as the home for the "PD separation is
net negative under agentic workloads" paper section: plot scripts for C1
(workload chars), C6 (roofline), C7 (routing-vs-PD-sep lever), the C6/C7
PDFs already rendered, and a README mapping candidate claims to required
figures plus open re-run items.

Removes --enforce-eager from bench.sh and all active launch scripts so
cuda graphs are captured -- the prior methodology suppressed one of
PD-sep's structural advantages (D-node fixed-shape decode). Legacy
scripts under scripts/legacy/ are intentionally untouched as historical
records.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

scripts/launch_elastic_p2p.sh

@@ -54,7 +54,7 @@ for i in $(seq 0 $((N_INSTANCES - 1))); do
     $VLLM serve "$MODEL" \
         --host 0.0.0.0 --port $port \
         --tensor-parallel-size 1 \
-        --trust-remote-code --enable-prefix-caching --enforce-eager \
+        --trust-remote-code --enable-prefix-caching \
         --dtype auto --gpu-memory-utilization 0.9 --max-model-len 200000 \
         --kv-transfer-config \
         '{"kv_connector":"MooncakeConnector","kv_role":"kv_both"}' \