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/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)