fix: reduce alarm snapshot label obstruction

tests/test_alarm_snapshots.py

@@ -189,6 +189,25 @@ class AlarmSnapshotTests(unittest.TestCase):
         dockerfile = (Path(__file__).resolve().parents[1] / "Dockerfile").read_text(encoding="utf-8")
         self.assertIn("fonts-noto-cjk", dockerfile)
 
+    def test_drawtext_label_style_stays_small_and_translucent(self) -> None:
+        filter_text = alarm_snapshots.build_drawtext_filter(
+            [
+                alarm_snapshots.OverlayLabel(
+                    text="区域 1",
+                    fallback_text="R1",
+                    x=10,
+                    y=20,
+                    accent_rgb=(255, 196, 0),
+                )
+            ],
+            Path("/tmp/NotoSansCJK-Regular.ttc"),
+            height=360,
+        )
+
+        self.assertIn("fontsize=13", filter_text)
+        self.assertIn("boxcolor=black@0.34", filter_text)
+        self.assertIn("boxborderw=2", filter_text)
+
     def test_capture_alert_snapshot_encodes_frame_with_configured_calibration_overlay(self) -> None:
         encoded_frames: list[Frame] = []