fix(发际线): 修正不对称刘海导致的模板叠加倾斜

按 MediaPipe 左右对应额头点协调模板延伸距离，保留人脸姿态与头部轮廓钳制，统一预览白线和生发遮罩的几何。补充对齐回归测试并更新贴图顺序测试及实现说明。

验证：13 项相关测试通过；两张用户图片完成前后对比，新图男性 7 型接口与生发图均成功返回。

tests/test_hairline.py

@@ -27,5 +27,9 @@ def test_mp_to_obj_anchor_mapping():
 
 def test_texture_map():
     m = get_texture_map()
-    assert [k for k, _ in m["female"]] == ["ellipse", "flower", "heart", "straight", "wave"]
-    assert [k for k, _ in m["male"]] == ["ellipse", "inverse_arc", "m", "straight"]
+    assert [k for k, _ in m["female"]] == [
+        "ellipse", "flower", "heart", "straight", "wave", "bigflower", "clasicalflower",
+    ]
+    assert [k for k, _ in m["male"]] == [
+        "ellipse", "inverse_arc", "m", "straight", "heart", "Softpetal", "wave",
+    ]

tests/test_hairline_alignment.py

@@ -0,0 +1,82 @@
+"""Template placement must follow face pose, not unequal left/right bangs."""
+import numpy as np
+import pytest
+
+from hairline import constants as C
+from hairline.hairline_2d import (
+    align_hairline_for_template,
+    clamp_hairline_to_silhouette,
+)
+
+
+def _scene(angle=0.0, shape=(600, 900)):
+    h, w = shape
+    scale = np.array([w, h])
+    lm = np.zeros((468, 3), np.float32)
+    xy = np.full((468, 2), [450.0, 300.0])
+    for i, (left, right) in enumerate(C.MP_TOP_ANCHOR_PAIRS):
+        xy[left] = [300.0 + i * 12, 210.0 - i * 8]
+        xy[right] = [600.0 - i * 12, 210.0 - i * 8]
+    xy[10] = [450, 150]
+    xy[152] = [450, 450]
+    theta = np.deg2rad(angle)
+    rotation = np.array([[np.cos(theta), -np.sin(theta)],
+                         [np.sin(theta), np.cos(theta)]])
+    xy = (xy - [450, 300]) @ rotation.T + [450, 300]
+    lm[:, :2] = xy / scale
+    up = rotation @ [0.0, -1.0]
+    anchors = lm[C.MP_TOP_ANCHORS, :2] * scale
+    distances = np.full(C.N_ANCHORS, 50.0)
+    indices = {k: i for i, k in enumerate(C.MP_TOP_ANCHORS)}
+    distances[indices[67]] = 80.0
+    distances[indices[297]] = 20.0
+    hairline = ((anchors + distances[:, None] * up) / scale).astype(np.float32)
+    return lm, hairline, np.ones(C.N_ANCHORS, bool), anchors, up
+
+
+@pytest.mark.parametrize("angle,shape", [(0, (600, 900)), (23, (600, 900)),
+                                         (-17, (1200, 900))])
+def test_uneven_bangs_do_not_shear_template(angle, shape):
+    lm, raw, valid, anchors, up = _scene(angle, shape)
+    raw_copy, lm_copy = raw.copy(), lm.copy()
+    aligned = align_hairline_for_template(lm, raw, valid, shape)
+    displacement = aligned * shape[::-1] - anchors
+    # Every anchor extends 50 px along the rotated face axis, even when
+    # one side's hair boundary is 60 px higher than its counterpart.
+    np.testing.assert_allclose(displacement, np.tile(50 * up, (C.N_ANCHORS, 1)), atol=1e-4)
+    np.testing.assert_array_equal(raw, raw_copy)
+    np.testing.assert_array_equal(lm, lm_copy)
+
+
+def test_anatomical_pairs_are_not_reversed_anchor_order():
+    shape = (600, 900)
+    lm, raw, valid, anchors, up = _scene(shape=shape)
+    # Endpoints of MP_TOP_ANCHORS are not mirror-ordered.
+    distances = {127: 10, 356: 30, 234: 60, 454: 100}
+    for mp_idx, distance in distances.items():
+        i = C.MP_TOP_ANCHORS.index(mp_idx)
+        raw[i] = (anchors[i] + distance * up) / shape[::-1]
+    aligned = align_hairline_for_template(lm, raw, valid, shape)
+    actual = (aligned * shape[::-1] - anchors) @ up
+    for mp_idx, expected in [(127, 20), (356, 20), (234, 80), (454, 80)]:
+        assert actual[C.MP_TOP_ANCHORS.index(mp_idx)] == pytest.approx(expected, abs=1e-4)
+
+
+def test_missing_ray_hit_does_not_pull_valid_partner():
+    shape = (600, 900)
+    lm, raw, valid, _anchors, _up = _scene(shape=shape)
+    left, right = C.MP_TOP_ANCHORS.index(67), C.MP_TOP_ANCHORS.index(297)
+    valid[right] = False
+    raw[right, 1] = -0.5  # An extrapolated fallback outside the head.
+    aligned = align_hairline_for_template(lm, raw, valid, shape)
+    np.testing.assert_allclose(aligned[[left, right]], raw[[left, right]], atol=1e-7)
+
+
+def test_template_alignment_still_allows_silhouette_clamping():
+    shape = (600, 900)
+    lm, raw, valid, _anchors, _up = _scene(shape=shape)
+    aligned = align_hairline_for_template(lm, raw, valid, shape)
+    parse_map = np.zeros(shape, np.int32)
+    parse_map[140:450, 250:650] = C.PARSE_SKIN
+    clamped = clamp_hairline_to_silhouette(aligned, parse_map)
+    assert np.min(clamped[:, 1] * shape[0]) >= 142 - 1e-4