feat(v1): chinese screenshot labels via Pillow with ASCII fallback

annotate_frame draws Chinese labels (e.g. '确认摔倒 P-0001') using a CJK
font via Pillow when available (Windows uses Microsoft YaHei), and falls
back to the ASCII cv2 label when Pillow or a CJK font is missing. 86 tests
pass.

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

v1/tests/test_alerts.py

@@ -4,12 +4,16 @@ from datetime import datetime, timezone
 import numpy as np
 import pytest
 
+import os
+
 from v1.alerts import (
     AlertDispatcher,
     AlertSink,
     EventArtifactWriter,
     annotate_frame,
+    annotation_label,
     screenshot_label,
+    _find_font,
 )
 from v1.fall_state import FallEvent, FallState
 from v1.view_model import MonitorViewState, PersonOverlay, Point, StatusColor
@@ -141,3 +145,34 @@ def test_annotate_draws_red_border_only_for_confirmed():
     corner = confirmed[0, 0].tolist()
     assert corner == [40, 40, 198]  # critical red in BGR
     assert confirmed.shape == image.shape
+
+
+def test_annotation_label_is_chinese():
+    assert annotation_label("P-0001", FallState.CONFIRMED) == "确认摔倒 P-0001"
+
+
+def test_find_font_returns_none_when_missing_and_path_when_present(tmp_path):
+    assert _find_font("/no/such/font.ttf") is None
+    font = tmp_path / "x.ttf"
+    font.write_bytes(b"stub")
+    assert _find_font(str(font)) == str(font)
+
+
+def test_annotate_falls_back_without_a_font():
+    image = np.full((60, 80, 3), 30, dtype=np.uint8)
+
+    out = annotate_frame(image, _confirmed_view(), font_path="/no/such/font.ttf")
+
+    assert out.shape == image.shape  # ASCII fallback ran, no crash
+
+
+def test_annotate_draws_labels_with_a_ttf_font():
+    font = "/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf"
+    if not os.path.isfile(font):
+        import pytest
+
+        pytest.skip("no ttf available to exercise the PIL path")
+
+    out = annotate_frame(np.full((60, 80, 3), 30, dtype=np.uint8), _confirmed_view(), font_path=font)
+
+    assert out.shape == (60, 80, 3)