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/workflow.md

@@ -176,6 +176,8 @@ Based on Step 2 content analysis, recommend a preset first (sets both type & sty
 - [Alternative preset] — [brief]
 - Or choose type manually: infographic / scene / flowchart / comparison / framework / timeline / mixed
 
+**Default**: if Step 2 found no strong content signal, the recommended preset MUST be `hand-drawn-edu` (infographic + sketch-notes + macaron — warm cream paper, black hand-drawn lines, soft pastel blocks). This is the universal fallback.
+
 **If user picks a preset → skip Q3** (type & style both resolved).
 **If user picks a type → Q3 is REQUIRED.**
 
@@ -203,13 +205,15 @@ If no `preferred_style` (present Core Styles first):
 
 | Core Style | Maps To | Best For |
 |------------|---------|----------|
+| `hand-drawn` | sketch-notes | **Default.** Warm cream paper, black hand-drawn lines, pastel blocks — educational infographics, concept explainers, onboarding, general knowledge articles |
 | `minimal-flat` | notion | General, knowledge sharing, SaaS |
 | `sci-fi` | blueprint | AI, frontier tech, system design |
-| `hand-drawn` | sketch/warm | Relaxed, reflective, casual |
 | `editorial` | editorial | Processes, data, journalism |
 | `scene` | warm/watercolor | Narratives, emotional, lifestyle |
 | `poster` | screen-print | Opinion, editorial, cultural, cinematic |
 
+**Default recommendation**: when Step 2 surfaces no strong content signal, recommend **`hand-drawn-edu`** preset (→ infographic + sketch-notes + macaron) as the primary option in Q1. When the user picks a type manually without a preferred_style, recommend `sketch-notes` first in Q3.
+
 Style selection based on Type × Style compatibility matrix (styles.md).
 **In Step 5.1**, read `styles/<style>.md` for visual elements and rendering rules.