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/eino-deep-dive.md

@@ -45,10 +45,6 @@ PreHandler 从全局 State 提取当前节点所需字段；PostHandler 将节
 
 QualitySupervisor 驱动的条件分支
 
-<div class="grid grid-cols-2 gap-4 mt-2">
-
-<div>
-
 ```go {1-10|all}
 g.AddBranch(nodeQualitySupervisor, compose.NewGraphBranch(
     func(ctx context.Context, _ PipelineInput) (string, error) {
@@ -67,9 +63,9 @@ g.AddBranch(nodeQualitySupervisor, compose.NewGraphBranch(
 ))
 ```
 
-</div>
+---
 
-<div class="flex flex-col justify-center">
+# 分支路由 — 逻辑与全貌
 
 <v-clicks>
 
@@ -84,9 +80,5 @@ g.AddBranch(nodeQualitySupervisor, compose.NewGraphBranch(
 </v-clicks>
 
 <div class="flex justify-center mt-2">
-  <img src="../public/pipeline-detail.svg" class="w-full max-h-[160px] object-contain" />
-</div>
-
-</div>
-
+  <img src="../public/pipeline-detail.svg" class="w-full max-h-[200px] object-contain" />
 </div>