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/solar_map_date_gate_test.go

@@ -0,0 +1,87 @@
+package svg
+
+import (
+	"strings"
+	"testing"
+	"time"
+
+	eclipsecore "b612.me/astro/eclipse"
+)
+
+// 核心判定当天无日食时，三个日食图入口都必须返回 false，与 LunarEclipseMapSVG 的日期门一致；
+// 偏食足迹是“取最近一次”语义，缺这道门会把邻近日期的图当成当天的图交出去。
+func TestSolarEclipseMapSVGRequiresEclipseOnDate(t *testing.T) {
+	type entry struct {
+		name   string
+		render func(time.Time, SolarEclipseMapSVGOptions) (string, bool)
+		global func(time.Time) (eclipsecore.SolarEclipseInfo, bool)
+	}
+	entries := []entry{
+		{
+			name:   "default",
+			render: SolarEclipseMapSVG,
+			global: eclipsecore.SolarEclipseOnDateNASABulletinSplitK,
+		},
+		{
+			name:   "nasaSplitK",
+			render: SolarEclipseMapSVGNASABulletinSplitK,
+			global: eclipsecore.SolarEclipseOnDateNASABulletinSplitK,
+		},
+		{
+			name:   "iauSingleK",
+			render: SolarEclipseMapSVGIAUSingleK,
+			global: eclipsecore.SolarEclipseOnDateIAUSingleK,
+		},
+	}
+	// 2024-04-08 是本组日期里唯一有日食的一天，其余都在最近一次日食前后半个朔望月内。
+	for _, test := range []struct {
+		day  string
+		want bool
+	}{
+		{day: "2024-04-08", want: true},
+		{day: "2024-04-15"},
+		{day: "2024-04-20"},
+		{day: "2024-04-23"},
+		{day: "2024-04-24"},
+	} {
+		date, err := time.Parse("2006-01-02", test.day)
+		if err != nil {
+			t.Fatalf("bad fixture date %q: %v", test.day, err)
+		}
+		for _, entry := range entries {
+			_, coreOK := entry.global(date)
+			if coreOK != test.want {
+				t.Fatalf("%s %s: core eclipse gate = %v, want %v", entry.name, test.day, coreOK, test.want)
+			}
+			rendered, ok := entry.render(date, SolarEclipseMapSVGOptions{
+				Width: 900, Height: 620, Location: time.UTC, PartialStep: 10 * time.Minute,
+			})
+			if ok != test.want {
+				t.Fatalf("%s %s: map gate = %v, want %v (core says %v)", entry.name, test.day, ok, test.want, coreOK)
+			}
+			if test.want && rendered == "" {
+				t.Fatalf("%s %s: gate passed but the map is empty", entry.name, test.day)
+			}
+			if !test.want && rendered != "" {
+				t.Fatalf("%s %s: rejected date still returned %d bytes", entry.name, test.day, len(rendered))
+			}
+		}
+	}
+}
+
+// 过了日期门的日期必须仍带完整等时线层：等时线自己还要查一次核心，门不能把它挡掉。
+func TestSolarEclipseMapOnDateKeepsIsochrones(t *testing.T) {
+	rendered, ok := SolarEclipseMapSVG(
+		time.Date(2024, time.April, 8, 0, 0, 0, 0, time.UTC),
+		SolarEclipseMapSVGOptions{
+			Width: 900, Height: 620, Location: time.UTC,
+			PartialStep: 10 * time.Minute, GreatestTimeStep: 30 * time.Minute,
+		},
+	)
+	if !ok {
+		t.Fatal("2024-04-08 is an eclipse date but the map was rejected")
+	}
+	if got := strings.Count(rendered, `class="solar-greatest-time-isoline"`); got != 7 {
+		t.Fatalf("isochrone paths = %d, want the full 7-branch fan", got)
+	}
+}