feat: 完善日月食与月掩几何链路并扩展历法接口

- 新增日月食中心带、偏食带、阴影足迹、等时线、食分线及升落边界计算，支持极区与混合食拓扑
- 新增日食单时刻阴影求解器、站心状态查询、批量采样和 ΔT 覆盖接口
- 重构恒星与行星月掩路径，补充有限盘面接触、站心修正、掩带宽度、极区投影及升落边界
- 扩展 SVG 与 GeoJSON 输出，支持详细面板、全球/极区/地球投影、边界闭合、时间标记和拓扑签名
- 扩展日月食候选搜索、局地搜索、沙罗序列预计算与范围外推，补充系列锚点和成员一致性校验
- 补齐古历纪年、儒略历独有闰日、多公历候选、历法改革跨日及精确日期运算接口
- 优化 ΔT、章动、恒星时、月球地平线、事件根搜索和本地星历缓存，降低重复计算开销并提升边界稳定

eclipse/svg/map_projection.go

@@ -3,6 +3,7 @@ package svg
 import "b612.me/astro/internal/svgmap"
 
 // EclipseMapProjection 控制全球日月食地图投影；零值根据事件几何选择投影。
+// 与 moon/svg.MapProjection 是同一概念的两套名字，取值字符串逐对相同。
 // EclipseMapProjection controls a global eclipse map projection. The zero value selects the projection from the event geometry.
 type EclipseMapProjection string
 
@@ -16,6 +17,9 @@ const (
 	// EclipseMapProjectionNorthPolar 使用北极方位等距投影。
 	// EclipseMapProjectionNorthPolar uses the north-polar azimuthal equidistant projection.
 	EclipseMapProjectionNorthPolar EclipseMapProjection = "north-polar"
+	// EclipseMapProjectionOrthographic 使用正射球面投影，视点取食甚点，只画朝向视点的半个地球。
+	// EclipseMapProjectionOrthographic uses the orthographic globe projection centred on the greatest point, drawing only the facing hemisphere.
+	EclipseMapProjectionOrthographic EclipseMapProjection = "orthographic"
 	// EclipseMapProjectionSouthPolar 使用南极方位等距投影。
 	// EclipseMapProjectionSouthPolar uses the south-polar azimuthal equidistant projection.
 	EclipseMapProjectionSouthPolar EclipseMapProjection = "south-polar"
@@ -28,7 +32,8 @@ func internalEclipseMapProjection(value EclipseMapProjection) svgmap.Projection
 func validEclipseMapProjection(value EclipseMapProjection) bool {
 	switch value {
 	case EclipseMapProjectionAuto, EclipseMapProjectionEquirectangular,
-		EclipseMapProjectionNorthPolar, EclipseMapProjectionSouthPolar:
+		EclipseMapProjectionNorthPolar, EclipseMapProjectionSouthPolar,
+		EclipseMapProjectionOrthographic:
 		return true
 	default:
 		return false
@@ -42,6 +47,8 @@ func eclipseMapProjectionLabel(projection svgmap.Projection, language string) st
 			return "North-polar azimuthal equidistant projection"
 		case svgmap.ProjectionSouthPolar:
 			return "South-polar azimuthal equidistant projection"
+		case svgmap.ProjectionOrthographic:
+			return "Orthographic globe projection, centred on the greatest eclipse; one hemisphere only"
 		default:
 			return "Equirectangular projection"
 		}
@@ -51,6 +58,8 @@ func eclipseMapProjectionLabel(projection svgmap.Projection, language string) st
 		return "北极方位等距投影"
 	case svgmap.ProjectionSouthPolar:
 		return "南极方位等距投影"
+	case svgmap.ProjectionOrthographic:
+		return "正射球面投影，视点取食甚点，只画朝向视点的半个地球"
 	default:
 		return "等经纬投影"
 	}