refactor(baoyu-cover-image): replace 20 styles with 5D palette×rendering system

Migrate from 4-dimension (Type×Style×Text×Mood) to 5-dimension
(Type×Palette×Rendering×Text×Mood) system. 9 palettes × 6 renderings
= 54 combinations replacing 20 fixed styles. Add style presets for
backward compatibility, v2→v3 schema migration, and new reference
structure (palettes/, renderings/, workflow/).

skills/baoyu-cover-image/references/renderings/painterly.md

@@ -0,0 +1,40 @@
+# painterly
+
+Soft, artistic, expressive
+
+## Core Characteristics
+
+Watercolor or paint-style illustration with visible brush strokes, color bleeds, and artistic texture. Feels like a hand-painted art piece.
+
+## Lines
+
+- Soft brush strokes with variable opacity
+- No hard outlines; edges defined by color transitions
+- Organic flowing strokes with natural blending
+
+## Texture
+
+- Visible paint or watercolor wash textures
+- Color bleeds and wet-on-wet effects
+- Paper texture showing through transparent areas
+- Brush stroke patterns visible
+
+## Depth
+
+- Soft edges with natural color blending
+- Atmospheric depth through color fading
+- Layered washes creating depth illusion
+
+## Element Vocabulary
+
+- Watercolor washes as backgrounds
+- Natural elements: leaves, flowers, organic forms
+- Soft gradients and color transitions
+- Splatter and drip effects as accents
+- Botanical and environmental motifs
+
+## Typography Approach
+
+- Elegant brush script or handwritten style
+- Organic letterforms with brush texture
+- Integrated with paint environment