feat: 完善时标与天象几何计算并扩展输出接口

- 新增时标、ΔT 模型、质心时间与 UT1 支持
- 改进日月食、月掩、行星事件及路径边界计算
- 完善恒星三维自行与动态距离传播
- 扩展 SVG、GeoJSON、KML 输出与底层距离换算工具
- 整理中英文手册、示例资源及回归测试

moon/svg/occultation_local_labels_test.go

@@ -0,0 +1,88 @@
+package svg
+
+import (
+	"testing"
+	"time"
+
+	"b612.me/astro/moon"
+)
+
+// 总览区接触标签契约：掠掩时四次接触只差几十角秒，标签必须自动避让排开，既不互相压叠、也不压到方位字、
+// 月球圆盘与右侧接触时刻栏；被推远的标签要用引线连回接触点。2026-09-14 保山月掩金星就是这种掠掩样本。
+
+const localOccultationOverviewLabelFill = "#792d28"
+
+func localPlanetOccultationOverviewLabels(t *testing.T, diagram string) []occultationSVGText {
+	t.Helper()
+	labels := []occultationSVGText{}
+	for _, text := range occultationSVGTexts(t, diagram) {
+		if text.fill == localOccultationOverviewLabelFill {
+			labels = append(labels, text)
+		}
+	}
+	return labels
+}
+
+func localOccultationOverviewLabelOverlaps(labels []occultationSVGText) [][2]string {
+	overlaps := [][2]string{}
+	for first := 0; first < len(labels); first++ {
+		for second := first + 1; second < len(labels); second++ {
+			a := occultationSVGTextBox(labels[first])
+			b := occultationSVGTextBox(labels[second])
+			if a[0] < b[2] && b[0] < a[2] && a[1] < b[3] && b[1] < a[3] {
+				overlaps = append(overlaps, [2]string{labels[first].value, labels[second].value})
+			}
+		}
+	}
+	return overlaps
+}
+
+func grazingVenusOccultation(t *testing.T) moon.PlanetOccultationInfo {
+	t.Helper()
+	location := time.FixedZone("CST", 8*3600)
+	events, err := moon.FindPlanetOccultations(
+		time.Date(2026, time.September, 14, 0, 0, 0, 0, location),
+		time.Date(2026, time.September, 15, 0, 0, 0, 0, location),
+		moon.OccultationVenus, 99.1611, 25.1120, 1650, moon.OccultationSearchOptions{},
+	)
+	if err != nil {
+		t.Fatalf("FindPlanetOccultations() error = %v", err)
+	}
+	if len(events) != 1 {
+		t.Fatalf("FindPlanetOccultations() returned %d events, want 1", len(events))
+	}
+	return events[0]
+}
+
+func TestLocalPlanetOccultationOverviewLabelsAvoidEachOther(t *testing.T) {
+	location := time.FixedZone("CST", 8*3600)
+	for _, tc := range []struct {
+		name  string
+		info  moon.PlanetOccultationInfo
+		width int
+		heigh int
+	}{
+		{"保山掠掩金星", grazingVenusOccultation(t), 935, 683},
+		{"土星全掩", localSaturnOccultation(t), 920, 720},
+	} {
+		diagram, err := LocalPlanetOccultationSVG(tc.info, LocalPlanetOccultationSVGOptions{
+			Width: tc.width, Height: tc.heigh, Location: location,
+		})
+		if err != nil {
+			t.Fatalf("%s: %v", tc.name, err)
+		}
+		labels := localPlanetOccultationOverviewLabels(t, diagram)
+		if len(labels) < 2 {
+			t.Fatalf("%s：总览区只有 %d 个接触标签", tc.name, len(labels))
+		}
+		if overlaps := localOccultationOverviewLabelOverlaps(labels); len(overlaps) > 0 {
+			t.Fatalf("%s：接触标签互相压叠 %v", tc.name, overlaps)
+		}
+		for _, text := range labels {
+			box := occultationSVGTextBox(text)
+			if box[0] < 0 || box[2] > float64(tc.width) || box[1] < 0 || box[3] > float64(tc.heigh) {
+				t.Fatalf("%s：标签「%s」越出画布 %v", tc.name, text.value, box)
+			}
+		}
+	}
+}