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

basic/occultation_instant.go

@@ -44,9 +44,8 @@ type PlanetOccultationInstant struct {
 	Total             *PlanetOccultationFootprint
 }
 
-// StarOccultationFootprintAt 返回指定时刻的精确点源恒星月掩可见足迹；它采用与路径时间线相同的分辨率，并对完整接触弧执行站心校正。
-// StarOccultationFootprintAt returns the exact visible lunar-occultation footprint of a point-source star at one instant, using timeline resolution and station-centred correction of the complete contact arc.
-func StarOccultationFootprintAt(at time.Time, star StarCoordinate) (StarOccultationInstant, error) {
+// StarOccultationFootprintAtWithInstance 用指定星历实例求值；inst 为 nil 时用进程当前模型 / evaluation with an explicit instance; nil uses the process model.
+func StarOccultationFootprintAtWithInstance(at time.Time, star StarCoordinate, inst *Instance) (StarOccultationInstant, error) {
 	result := StarOccultationInstant{Time: at, TargetID: star.ID}
 	if at.IsZero() {
 		return result, fmt.Errorf("%w: time is required", ErrInvalidOccultationInput)
@@ -55,7 +54,7 @@ func StarOccultationFootprintAt(at time.Time, star StarCoordinate) (StarOccultat
 		return result, err
 	}
 
-	cache := newStarOccultationEventCache(star)
+	cache := newStarOccultationEventCache(star, inst)
 	tt := occultationTimeToTT(at)
 	result.DeltaTSeconds = DeltaT(tt, true)
 	result.SublunarLongitude, result.SublunarLatitude = occultationSublunarPoint(tt, cache.frameAt)
@@ -65,9 +64,8 @@ func StarOccultationFootprintAt(at time.Time, star StarCoordinate) (StarOccultat
 	return result, nil
 }
 
-// PlanetOccultationFootprintsAt 返回指定时刻有限行星盘面的精确外接触和内接触月掩可见足迹；它采用路径时间线分辨率，并对每条完整接触弧执行站心校正。
-// PlanetOccultationFootprintsAt returns the exact visible outer- and inner-contact lunar-occultation footprints of a finite planetary disk at one instant, using timeline resolution and station-centred correction of each complete contact arc.
-func PlanetOccultationFootprintsAt(at time.Time, planet OccultationPlanet) (PlanetOccultationInstant, error) {
+// PlanetOccultationFootprintsAtWithInstance 用指定星历实例求值；inst 为 nil 时用进程当前模型 / evaluation with an explicit instance; nil uses the process model.
+func PlanetOccultationFootprintsAtWithInstance(at time.Time, planet OccultationPlanet, inst *Instance) (PlanetOccultationInstant, error) {
 	result := PlanetOccultationInstant{Time: at, Planet: planet, TargetID: planet.String()}
 	if at.IsZero() {
 		return result, fmt.Errorf("%w: time is required", ErrInvalidOccultationInput)
@@ -76,8 +74,8 @@ func PlanetOccultationFootprintsAt(at time.Time, planet OccultationPlanet) (Plan
 		return result, err
 	}
 
-	config, _ := planetOccultationConfigFor(planet)
-	cache := newPlanetOccultationEventCache(config)
+	config, _ := planetOccultationConfigFor(planet, inst)
+	cache := newPlanetOccultationEventCache(config, inst)
 	tt := occultationTimeToTT(at)
 	result.DeltaTSeconds = DeltaT(tt, true)
 	result.SublunarLongitude, result.SublunarLatitude = occultationSublunarPoint(tt, cache.outerFrameAt)