feat: 引入可切换星历模型并扩展天象观测链路

- 新增半解析、旧模型、自定义与多源堆叠星历实例，提供 Context、Instance、SPK 读取及状态与视位置计算
- 统一太阳、月球和行星实例接口，扩展黄经穿越、留、相位、最近角距、偕日可见、任意高度升落、轨道节点及凌日等天象查询
- 完善日月食、月掩与凌日的月缘剖面、有限盘面接触、站心修正、局地可见性、全球路径和地图输出
- 新增 SVG、GeoJSON、KML 天象输出及凌日、月掩和月缘地形相关缓存与几何求解
- 新增恒星星表导入与查询，支持 CSV、Hipparcos、BSC5、Stellarium 等格式及名称、交叉标识、锥面检索和星等过滤
- 补充 IAU 2006、地球定向、折射消光、大气观测、轨道传播及半解析行星/月球数据支持
- 将默认未来民用时标切换为 TimeScaleLeapHour，更新 2027–2400 农历速查表、中文日期解析和时区边界处理
- 增加事件基线、跨模型回归、几何边界、月缘地形和输出契约测试，完善中英文手册、示例资源、NOTICE 与忽略规则

internal/occultationgeo/direct_band.go

@@ -39,8 +39,8 @@ func DirectVisibleBandPolygons(
 		}
 		if len(samples) > 0 {
 			previous := samples[len(samples)-1]
-			direct := geoDistanceKM(previous.a, boundary[0]) + geoDistanceKM(previous.b, boundary[len(boundary)-1])
-			swapped := geoDistanceKM(previous.a, boundary[len(boundary)-1]) + geoDistanceKM(previous.b, boundary[0])
+			direct := geodata.EquatorialDistanceKM(previous.a, boundary[0]) + geodata.EquatorialDistanceKM(previous.b, boundary[len(boundary)-1])
+			swapped := geodata.EquatorialDistanceKM(previous.a, boundary[len(boundary)-1]) + geodata.EquatorialDistanceKM(previous.b, boundary[0])
 			if swapped < direct {
 				reverseGeoPoints(boundary)
 			}
@@ -140,7 +140,7 @@ func removeDirectProjectedSharpCorners(
 		changed := false
 		for index := 1; index+1 < len(result); index++ {
 			first, middle, last := result[index-1], result[index], result[index+1]
-			if geoDistanceKM(first, last) > maximumChordKM {
+			if geodata.EquatorialDistanceKM(first, last) > maximumChordKM {
 				continue
 			}
 			scale := math.Cos(middle.Latitude * math.Pi / 180)
@@ -281,7 +281,7 @@ func reverseGeoPoints(points []geodata.GeoPoint) {
 }
 
 func appendDirectRingPoint(ring *[]geodata.GeoPoint, point geodata.GeoPoint) {
-	if len(*ring) > 0 && geoDistanceKM((*ring)[len(*ring)-1], point) <= 1e-6 {
+	if len(*ring) > 0 && geodata.EquatorialDistanceKM((*ring)[len(*ring)-1], point) <= 1e-6 {
 		return
 	}
 	*ring = append(*ring, point)
@@ -299,7 +299,7 @@ func densifyDirectRing(ring []geodata.GeoPoint, maximumEdgeKM float64) []geodata
 		}
 		next := ring[index+1]
 		steps := int(math.Ceil(math.Max(
-			geoDistanceKM(point, next), occultationProjectedEdgeDistanceKM(point, next),
+			geodata.EquatorialDistanceKM(point, next), geodata.WebMercatorDistanceKM(point, next),
 		) / maximumEdgeKM))
 		if steps < 2 {
 			continue