feat(baoyu-article-illustrator): default to sketch-notes educational infographic style

Make `hand-drawn-edu` (infographic + sketch-notes + macaron) the universal
fallback preset when content analysis surfaces no strong signal. Rework
sketch-notes style spec around warm cream paper + black hand-drawn lines +
soft pastel section blocks.

- Change `hand-drawn-edu` preset type from flowchart to infographic; add
  `hand-drawn-edu-flow` (flowchart) and `hand-drawn-edu-compare` (comparison)
  as variants for users who need those layouts in the same warm style
- Elevate `sketch-notes` to primary style across infographic / flowchart /
  comparison / framework auto-selection; add sketch-notes column to
  Type x Style compatibility matrix
- Rewrite sketch-notes.md: macaron pastel palette, canonical single-page
  layout (title / sectioned boxes / takeaway), diagram-only rule
- Add infographic + sketch-notes + macaron prompt block to
  prompt-construction.md
- Update workflow, style-presets, and first-time-setup defaults to match

skills/baoyu-article-illustrator/references/config/first-time-setup.md

@@ -61,8 +61,10 @@ Position defaults to bottom-right.
 header: "Style"
 question: "Default illustration style preference? Or type another style name or your custom style"
 options:
-  - label: "None (Recommended)"
-    description: "Auto-select based on content analysis"
+  - label: "sketch-notes (Recommended)"
+    description: "Warm cream paper, black hand-drawn lines, soft pastel blocks — educational infographic feel. Great default for most articles."
+  - label: "None"
+    description: "Auto-select based on content analysis (falls back to sketch-notes when no strong signal)"
   - label: "notion"
     description: "Minimalist hand-drawn line art"
   - label: "warm"