feat(baoyu-article-illustrator): add screen-print style and style presets

Add screen-print as new style option with poster aesthetic (bold silhouettes,
halftone textures, limited colors). Add --preset flag for quick type + style
selection (e.g., --preset tech-explainer, --preset opinion-piece).

skills/baoyu-article-illustrator/references/style-presets.md

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+# Style Presets
+
+`--preset X` expands to a type + style combination. Users can override either dimension.
+
+| --preset | Type | Style |
+|----------|------|-------|
+| `tech-explainer` | `infographic` | `blueprint` |
+| `knowledge-base` | `infographic` | `vector-illustration` |
+| `saas-guide` | `infographic` | `notion` |
+| `data-report` | `infographic` | `editorial` |
+| `science-paper` | `infographic` | `scientific` |
+| `tutorial` | `flowchart` | `vector-illustration` |
+| `process-flow` | `flowchart` | `notion` |
+| `system-design` | `framework` | `blueprint` |
+| `architecture` | `framework` | `vector-illustration` |
+| `versus` | `comparison` | `vector-illustration` |
+| `business-compare` | `comparison` | `elegant` |
+| `storytelling` | `scene` | `warm` |
+| `lifestyle` | `scene` | `watercolor` |
+| `history` | `timeline` | `elegant` |
+| `evolution` | `timeline` | `warm` |
+| `opinion-piece` | `scene` | `screen-print` |
+| `editorial-poster` | `comparison` | `screen-print` |
+| `cinematic` | `scene` | `screen-print` |
+
+## Override Examples
+
+- `--preset tech-explainer --style notion` = infographic type with notion style
+- `--preset storytelling --type timeline` = timeline type with warm style
+
+Explicit `--type`/`--style` flags always override preset values.