feat: 完善时标与天象几何计算并扩展输出接口

- 新增时标、ΔT 模型、质心时间与 UT1 支持
- 改进日月食、月掩、行星事件及路径边界计算
- 完善恒星三维自行与动态距离传播
- 扩展 SVG、GeoJSON、KML 输出与底层距离换算工具
- 整理中英文手册、示例资源及回归测试

eclipse/solar_path.go

@@ -44,6 +44,12 @@ type SolarEclipsePathPoint struct {
 type SolarEclipsePath struct {
 	// Eclipse 是对应的全局日食信息, related global solar eclipse information.
 	Eclipse SolarEclipseInfo
+	// PathWidthDefined 表示本结果的带宽是否有定义：两限存在且上下两条限界线都非空时才为 true；
+	// 为 false 时 Eclipse.PathWidthKM 与 Greatest.WidthKM 都是 0。
+	// PathWidthDefined reports whether this result has a defined band width: both
+	// limits must exist and both limit lines must be non-empty. When it is false,
+	// Eclipse.PathWidthKM and Greatest.WidthKM are 0.
+	PathWidthDefined bool
 	// Greatest 是食甚点/最佳观测点, greatest eclipse point.
 	Greatest SolarEclipsePathPoint
 	// CenterLine 是中心线, central line.
@@ -333,6 +339,7 @@ func solarEclipseCentralPath(
 
 	path := SolarEclipsePath{
 		Eclipse:                     solarEclipseInfoFromBasic(result.Eclipse, location),
+		PathWidthDefined:            result.PathWidthDefined,
 		Greatest:                    solarEclipsePathPointFromBasic(result.Greatest, location),
 		CenterLine:                  solarEclipsePathPointsFromBasic(result.CenterLine, location),
 		NorthernLimit:               solarEclipsePathPointsFromBasic(result.NorthernLimit, location),