fix: split overflowing slides to fit frankfurt theme header/footer bars

- eino-deep-dive.md: split slide 2 into code-only + explanation+SVG slides
- async-deep-dive.md: split slide 2 into code-only + progress+SVG slides
- harness.md: split slide 2 (4 Items + SVG) into two slides (2 Items each)
- request-journey.md: split into middleware/handler + pipeline/finalization slides

The frankfurt theme header (~40px) overlaps ~7px into the content zone,
leaving ~467px effective height. Dense slides with code+Items+images
exceeded this budget and were hidden behind the bars.

decks/gen2D/pages/request-journey.md

@@ -10,10 +10,6 @@ POST /api/v1/generate  {prompt: "像素风骑士", assetType: "sprite", style: {
 
 </div>
 
-<div class="grid grid-cols-2 gap-4 mt-2">
-
-<div>
-
 <v-clicks>
 
 <Item title="① Middleware 层（~1ms）">
@@ -26,9 +22,11 @@ JWT 认证 → 解析 userID → 用户级限流（Redis Lua）→ 全局限流
 
 </v-clicks>
 
-</div>
+---
 
-<div>
+# 请求旅程 — 管线执行与收尾
+
+耗时集中在管线阶段（~30s 占 95%）
 
 <v-clicks>
 
@@ -42,11 +40,7 @@ goroutine 取任务 → PromptOptimizer → AssetGenerator → QualitySupervisor
 
 </v-clicks>
 
-</div>
-
-</div>
-
-<div v-click class="mt-2 text-center text-gray-400 text-sm">
+<div v-click class="mt-4 text-center text-gray-400 text-sm">
   全程异步：前端拿到 taskId 后通过 WebSocket 实时监听进度变化
 </div>