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/lunarhorizon/lunarhorizon.go

@@ -18,18 +18,10 @@ import (
 	"time"
 
 	"b612.me/astro/basic"
+	"b612.me/astro/internal/ephem"
 	"b612.me/astro/internal/geodata"
 )
 
-// normalizeLongitude 把经度归一化到 [-180, 180)；internal/geodata 与 geojson 各有一份等价的未导出实现，无法跨包复用。
-func normalizeLongitude(value float64) float64 {
-	value = math.Mod(value+180, 360)
-	if value < 0 {
-		value += 360
-	}
-	return value - 180
-}
-
 // defaultToleranceDegrees 是 GeoJSON 导出使用的误差门限。GeoJSON 客户端可以无限放大，
 // 因此这里取远小于任何地图像素的角度。
 // defaultToleranceDegrees is the error tolerance used by the GeoJSON export. GeoJSON clients
@@ -47,7 +39,12 @@ const DefaultToleranceDegrees = defaultToleranceDegrees
 // longitude. Refine in map coordinates before clipping; extra vertices are
 // corrected to the same topocentric zero-altitude curve as the source ring.
 func Refine(points []geodata.GeoPoint, at time.Time) []geodata.GeoPoint {
-	return RefineWithin(points, at, defaultToleranceDegrees)
+	return RefineWithInstance(points, at, nil)
+}
+
+// RefineWithInstance 指定星历实例的站心地平线细分 / topocentric horizon refinement with an explicit instance.
+func RefineWithInstance(points []geodata.GeoPoint, at time.Time, inst *ephem.Instance) []geodata.GeoPoint {
+	return RefineWithinWithInstance(points, at, defaultToleranceDegrees, inst)
 }
 
 // RefineWithin 用给定误差门限（单位：度）细分一条站心地平线。插入的顶点被校正回零高度，
@@ -58,6 +55,11 @@ func Refine(points []geodata.GeoPoint, at time.Time) []geodata.GeoPoint {
 // accuracy without moving the curve. A fixed-resolution target such as an SVG map can pass a
 // tolerance matched to its pixel scale instead of emitting vertices no display can resolve.
 func RefineWithin(points []geodata.GeoPoint, at time.Time, toleranceDegrees float64) []geodata.GeoPoint {
+	return RefineWithinWithInstance(points, at, toleranceDegrees, nil)
+}
+
+// RefineWithinWithInstance 指定星历实例和误差门限的站心地平线细分 / topocentric horizon refinement with an explicit instance and tolerance.
+func RefineWithinWithInstance(points []geodata.GeoPoint, at time.Time, toleranceDegrees float64, inst *ephem.Instance) []geodata.GeoPoint {
 	if !(toleranceDegrees > 0) {
 		toleranceDegrees = defaultToleranceDegrees
 	}
@@ -66,10 +68,10 @@ func RefineWithin(points []geodata.GeoPoint, at time.Time, toleranceDegrees floa
 	}
 	jd := basic.Date2JD(at.UTC())
 	tt := basic.UTC2TT(jd)
-	ra, dec := basic.HMoonTrueRaDec(tt)
-	distanceAU := basic.HMoonAway(tt) / 149597870.7
+	ra, dec := basic.HMoonTrueRaDecWithInstance(tt, inst)
+	distanceAU := basic.HMoonAwayWithInstance(tt, inst) / 149597870.7
 	sidereal := basic.ApparentSiderealTime(basic.UTC2UT1(jd)) * 15
-	center := geodata.GeoPoint{Longitude: normalizeLongitude(ra - sidereal), Latitude: dec}
+	center := geodata.GeoPoint{Longitude: geodata.NormalizeLongitude(ra - sidereal), Latitude: dec}
 	// Every correction is at the same instant. Reuse its full ephemeris while
 	// retaining the ellipsoid and topocentric transform used by HMoonHeight.
 	altitudeAt := func(point geodata.GeoPoint) float64 {