Replace max/median hotspot index with (median, max) absolute pair

The max/median ratio inverts the actual user-facing p90 ranking:
  sticky:  hotspot=2.73 but system e2e p90 = 34.6s  (worst)
  unified: hotspot=3.67 but system e2e p90 = 18.0s  (best)
because sticky's median is also high (everyone slow) while unified
concentrates the damage on one worker and keeps the other 7 fast.
Any "imbalance" metric structurally punishes the affinity-then-escape
schemes that we actually want to advocate for.

Changes:
- analysis/characterization/render_window1_figures.py:
  fig_b3_per_worker_ttft now annotates each subplot with
  "median X.Xs · max Y.Ys" instead of "hotspot=Y.YY"; docstring
  documents why we drop the ratio.
- figs/f4c_per_worker_ttft.png: regenerated with new titles.
- figs/f4c_apc_vs_hotspot_tradeoff.png: deleted. The scatter's y-axis
  was the deprecated ratio; superseded by f4c per-worker bars + f6
  e2e bars which together carry the same information honestly.
- PAPER_OUTLINE.md: C3, §3.3, §4.1 wording, §5 metric list, §8
  conclusion — replace "hotspot index" mentions with
  "worst-worker p90" or "(median, max) worker p90"; promote the
  §3.3 methodology note to a top-level sub-finding ("hot pin
  failure must be measured with per-worker absolute latency,
  not normalized ratio").
- MEETING.md: §3.3 narrative reworded to lead with the (median, max)
  pair directly; explicit one-line note on why the ratio is dropped.

Conceptual uses of "hot session" / "hot instance" / "hot pin" remain
unchanged — only the *metric* called hotspot index is retired.

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

MEETING.md

@@ -51,7 +51,7 @@ agentic 平均请求 33.6k token 需 3.3GB KV；4P+4D / 6P+2D 在 agentic regime
 
 ![](figs/f4c_per_worker_ttft.png)
 
-注意 hotspot index（max/median 比值）单独看会误导：sticky 的 hotspot=2.73 比 unified 的 3.67 *低*，但**绝对值**告诉我们 sticky 是"全员一起慢"，unified 是"一个 worker 牺牲、其他 7 个快"：
+我们刻意 **用 (median, max) 两个绝对数**衡量 worker 不平衡，不用 `max/median` 单一比值 —— 比值会把 unified（一个 worker 牺牲、其他 7 个快）算成比 sticky（全员一起慢）更不平衡，与系统 e2e p90 实际排序反向。下面是绝对数：
 
 | | median worker TTFT p90 | max worker | system e2e p90 |
 |---|---:|---:|---:|