修复: 技能面板视口按行收口与截断尾部乱码

- 技能列表视口改按行数切片（含描述行），修复变长条目撑爆面板
- 大文件截断改按 rune 边界回退，修复中文内容尾部乱码
- 补视口与截断边界测试

internal/view_skills.go

@@ -65,10 +65,16 @@ func (m *Model) skillsListLines(w, listH int) []string {
 	if len(skills) == 0 {
 		return []string{style.DimFg.Render(fitWidth("  empty", w))}
 	}
-	start, end := viewport(m.Skills.SkillCur, len(skills), listH)
-	var lines []string
-	for i := start; i < end; i++ {
-		sk := skills[i]
+	// 先为所有技能累积全部行（含描述行），再按行数视口切片，
+	// 避免按条目数计算视口导致变长行撑爆面板
+	type skillBlock struct {
+		lines []string
+	}
+	var blocks []skillBlock
+	totalLines := 0
+	curLineOffset := 0
+
+	for i, sk := range skills {
 		cur := " "
 		if i == m.Skills.SkillCur {
 			cur = "▸"
@@ -78,7 +84,7 @@ func (m *Model) skillsListLines(w, listH int) []string {
 		if i == m.Skills.SkillCur && m.Skills.FocusPanel == 0 {
 			sty = style.SelStyle
 		}
-		lines = append(lines, sty.Render(padRightByWidth(truncateByWidth(line, w), w)))
+		blockLines := []string{sty.Render(padRightByWidth(truncateByWidth(line, w), w))}
 		// 如果有描述，追加一行
 		if sk.Description != "" {
 			descLine := "   " + sk.Description
@@ -86,10 +92,25 @@ func (m *Model) skillsListLines(w, listH int) []string {
 			if i == m.Skills.SkillCur && m.Skills.FocusPanel == 0 {
 				descSty = style.SelStyle
 			}
-			lines = append(lines, descSty.Render(padRightByWidth(truncateByWidth(descLine, w), w)))
+			blockLines = append(blockLines, descSty.Render(padRightByWidth(truncateByWidth(descLine, w), w)))
 		}
+		if i == m.Skills.SkillCur {
+			curLineOffset = totalLines
+		}
+		totalLines += len(blockLines)
+		blocks = append(blocks, skillBlock{lines: blockLines})
 	}
-	return lines
+
+	start, end := viewport(curLineOffset, totalLines, listH)
+
+	var allLines []string
+	for _, b := range blocks {
+		allLines = append(allLines, b.lines...)
+	}
+	if end > len(allLines) {
+		end = len(allLines)
+	}
+	return allLines[start:end]
 }
 
 func (m *Model) skillsFileLines(w, listH int) []string {