fix(annotation): 标注图重排，8 个量全标注且不重叠

- 修复七眼三个横向量(单眼宽度/两眼间距/脸宽)叠在同一条眼睛线上的重叠问题，
  改为上下错开三个高度，各自虚线带箭头 + 紧贴标签
- 新增「全脸总高」标注：右侧竖向标尺(虚线双箭头，头顶→下巴)+ 标签
- 四庭(顶/上/中/下庭)仍在左侧各段中点
- 标签用全名：单眼宽度/两眼间距/脸宽/全脸总高
- 新增 tests/test_annotation.py 防回归

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_annotation.py

@@ -0,0 +1,30 @@
+"""标注图生成测试：RGBA 透明底 + 尺寸 + 有内容（不重叠由人工目视核验）。"""
+import cv2
+import numpy as np
+from conftest import fixture
+
+from face_analysis.detector import detector
+from face_analysis.measure import measure_face
+from face_analysis.annotation import create_annotated_image
+
+
+def test_annotation_rgba_transparent():
+    img = cv2.imread(fixture("frontal.jpg"))
+    h, w = img.shape[:2]
+    lms = detector.detect(img)
+    r = measure_face(lms, None, w, h)   # 方案A，确定性
+    canvas = create_annotated_image(img, r)
+    assert canvas.mode == "RGBA"
+    assert canvas.size == (w, h)
+    arr = np.asarray(canvas)
+    assert (arr[:, :, 3] == 0).any()    # 存在透明像素
+    assert (arr[:, :, 3] > 0).any()     # 存在不透明像素（线/字）
+
+
+def test_annotation_runs_on_hard_sample():
+    img = cv2.imread(fixture("hard_longhair.jpg"))
+    h, w = img.shape[:2]
+    lms = detector.detect(img)
+    r = measure_face(lms, None, w, h)
+    canvas = create_annotated_image(img, r)
+    assert canvas.size == (w, h)