支持板块图标与主题色自定义，并优化列表加载与未保存离开提示。

新增后端图标校验与色槽规范化，前端展示 BoardBadge/骨架屏，发帖与板块管理页增加未保存确认。

Co-authored-by: Cursor <cursoragent@cursor.com>

service/board_icon.go

@@ -0,0 +1,36 @@
+package service
+
+import "strings"
+
+// AllowedBoardIcons 与前端 BOARD_ICON_OPTIONS 的 key 保持一致
+var AllowedBoardIcons = map[string]struct{}{
+	"code-2": {}, "coffee": {}, "help-circle": {}, "message-square": {},
+	"lightbulb": {}, "book-open": {}, "gamepad-2": {}, "palette": {},
+	"music": {}, "camera": {}, "heart": {}, "zap": {},
+	"globe": {}, "users": {}, "briefcase": {}, "graduation-cap": {},
+	"shopping-bag": {}, "map-pin": {}, "megaphone": {}, "flame": {},
+	"star": {}, "folder": {}, "wrench": {}, "cpu": {},
+}
+
+// NormalizeBoardIcon 校验并规范化板块图标 key，非法或空则返回空串
+func NormalizeBoardIcon(icon string) string {
+	icon = strings.TrimSpace(strings.ToLower(icon))
+	if icon == "" {
+		return ""
+	}
+	if _, ok := AllowedBoardIcons[icon]; !ok {
+		return ""
+	}
+	return icon
+}
+
+// NormalizeBoardColorIndex -1 表示自动；0–7 为有效色槽
+func NormalizeBoardColorIndex(colorIndex int) int {
+	if colorIndex < 0 {
+		return -1
+	}
+	if colorIndex > 7 {
+		return colorIndex % 8
+	}
+	return colorIndex
+}