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/dimensions/mood.md

@@ -102,15 +102,29 @@ Dynamic, high-impact visual presence.
 
 ✓✓ = highly recommended | ✓ = compatible | ✗ = not recommended
 
-## Style Interaction
+## Palette Interaction
 
-Mood modifies the base style characteristics:
+Mood modifies the base palette characteristics:
 
-| Style Category | subtle | balanced | bold |
-|----------------|--------|----------|------|
-| Technical (blueprint, notion) | Lighter lines, softer colors | Standard rendering | Stronger contrast, sharper edges |
-| Artistic (watercolor, sketch-notes) | More whitespace, lighter strokes | Standard rendering | Deeper colors, heavier strokes |
-| Editorial (bold-editorial, dark-atmospheric) | Reduced contrast, softer tones | Standard rendering | Maximum impact, vivid colors |
+| Palette Category | subtle | balanced | bold |
+|------------------|--------|----------|------|
+| Warm palettes (warm, earth, pastel) | More whitespace, softer tones | Standard colors | Deeper, richer warm tones |
+| Cool palettes (cool, mono, elegant) | Lighter lines, muted colors | Standard colors | Stronger contrast, sharper definition |
+| Dark palettes (dark, vivid) | Reduced contrast, softer glow | Standard colors | Maximum impact, vivid saturation |
+| Vintage palettes (retro) | More faded, sepia-heavy | Standard colors | Bolder retro contrasts |
+
+## Rendering Interaction
+
+Mood adjusts rendering characteristics:
+
+| Rendering | subtle | balanced | bold |
+|-----------|--------|----------|------|
+| flat-vector | Thinner strokes, lighter fills | Standard weight | Thicker strokes, stronger fills |
+| hand-drawn | Lighter pencil pressure, more space | Standard strokes | Heavier marker strokes, denser elements |
+| painterly | Diluted washes, more white | Standard brush | Thicker paint, saturated strokes |
+| digital | Reduced shadows, lower contrast | Standard rendering | Stronger shadows, sharper edges |
+| pixel | Fewer colors, simpler shapes | Standard palette | More colors, denser pixel detail |
+| chalk | Lighter chalk, more board showing | Standard chalk | Heavy chalk, vivid colors, dense marks |
 
 ## Auto Selection
 

skills/baoyu-cover-image/references/dimensions/text.md

@@ -49,8 +49,18 @@ Single headline, maximum impact.
 
 **Title Guidelines**:
 - Punchy, action-oriented
-- Numbers, questions, contrasts work well
 - Match content language
+- Use engagement hooks (see below)
+
+**Engagement Hooks**:
+
+| Hook Type | Examples (EN) | Examples (ZH) |
+|-----------|---------------|---------------|
+| Numbers | "3 Traps", "5 Keys" | "3个陷阱", "5个关键" |
+| Questions | "Why X?", "How?" | "为什么X?", "怎么做?" |
+| Contrasts | "A vs B", "Old→New" | "A还是B", "旧→新" |
+| Pain Points | "Stop X", "Never Do" | "别再X了", "千万别" |
+| Suspense | "Hidden X", "Secret" | "隐藏的X", "秘密" |
 
 ### title-subtitle
 
@@ -67,6 +77,10 @@ Title with supporting context.
 - Reserved zone: 25%
 - Clear hierarchy between title/subtitle
 
+**Title Guidelines**:
+- Use engagement hooks: numbers, questions, contrasts, pain points, suspense
+- Punchy, action-oriented
+
 **Subtitle Guidelines**:
 - Clarify or contextualize title
 - Can include series name, author, date
@@ -89,6 +103,10 @@ Information-dense cover with multiple text elements.
 - Reserved zone: 40%
 - Clear visual hierarchy
 
+**Title Guidelines**:
+- Use engagement hooks: numbers, questions, contrasts, pain points, suspense
+- Punchy, action-oriented
+
 **Tag Guidelines**:
 - 2-4 tags maximum
 - Short keywords (1-2 words each)