feat: 新增月掩与日月食地理绘图并提升观测计算精度

- 新增月掩恒星和行星：支持搜索、掩甚点、全球掩带及固定地点轨迹计算
- 支持恒星星表坐标转换、有限盘面行星接触事件和月掩 SVG 输出
- 新增日月食及月掩全球投影图、时间标记和 GeoJSON 地理数据接口
- 扩展日食中心线、南北界及偏食足迹采样，支持极区投影
- 修正站心时角、月出月落、月球视半径、折射和恒星自行计算
- 优化内外行星事件搜索、边界选择、极端输入处理和计算稳定性

internal/svgmap/map_test.go

@@ -0,0 +1,51 @@
+package svgmap
+
+import (
+	"math"
+	"strings"
+	"testing"
+)
+
+func TestPolarProjectionPlacesPoleAtCenterAndEquatorOnFrame(t *testing.T) {
+	frame := Frame{X: 10, Y: 20, Width: 300, Height: 300, Projection: ProjectionNorthPolar}
+	x, y, ok := frame.Project(123, 90)
+	if !ok || math.Abs(x-160) > 1e-9 || math.Abs(y-170) > 1e-9 {
+		t.Fatalf("north pole = %.3f %.3f %v, want map center", x, y, ok)
+	}
+	x, y, ok = frame.Project(0, 0)
+	if !ok || math.Abs(x-160) > 1e-9 || math.Abs(y-20) > 1e-9 {
+		t.Fatalf("prime-meridian equator = %.3f %.3f %v, want top edge", x, y, ok)
+	}
+	if _, _, ok := frame.Project(0, -1); ok {
+		t.Fatal("north-polar projection accepted a southern-hemisphere point")
+	}
+}
+
+func TestProjectionClippingDoesNotSplitPolarAntimeridian(t *testing.T) {
+	points := []GeoPoint{{Longitude: 170, Latitude: 70}, {Longitude: -170, Latitude: 70}}
+	segments := PolylineSegments(points, ProjectionNorthPolar)
+	if len(segments) != 1 || len(segments[0]) != 2 {
+		t.Fatalf("polar antimeridian segments = %#v, want one continuous segment", segments)
+	}
+	segments = PolylineSegments(points, ProjectionEquirectangular)
+	if len(segments) != 2 {
+		t.Fatalf("equirectangular antimeridian segment count = %d, want 2", len(segments))
+	}
+}
+
+func TestNaturalEarthAssetsAndPolarClip(t *testing.T) {
+	if len(equirectangularLandPath) < 150000 || len(northPolarLandPath) < 100000 || len(southPolarLandPath) < 40000 {
+		t.Fatalf("unexpected embedded map sizes: world=%d north=%d south=%d",
+			len(equirectangularLandPath), len(northPolarLandPath), len(southPolarLandPath))
+	}
+	frame := Frame{Width: 300, Height: 300, Projection: ProjectionSouthPolar}
+	var builder strings.Builder
+	frame.WriteOcean(&builder)
+	frame.WriteLand(&builder, "clip")
+	frame.WriteFrame(&builder)
+	for _, want := range []string{`class="map-ocean"`, `class="land"`, `class="map-frame"`, `<circle`} {
+		if !strings.Contains(builder.String(), want) {
+			t.Fatalf("polar map output missing %q", want)
+		}
+	}
+}