feat: add cold display alarm flow and labeled snapshots

tests/test_alarm_snapshots.py

@@ -2,10 +2,12 @@ from __future__ import annotations
 
 import unittest
 from datetime import datetime, timezone
+from pathlib import Path
 
 from cold_display_guard import alarm_snapshots
 from cold_display_guard.alarm_snapshots import (
     capture_alert_snapshot,
+    fallback_label_text,
     load_alarm_snapshot_settings,
     upload_snapshot_bytes,
 )
@@ -153,6 +155,40 @@ class AlarmSnapshotTests(unittest.TestCase):
         self.assertNotEqual(annotated.pixel(2, 2), (0, 0, 0))
         self.assertNotEqual(annotated.pixel(0, 0), (0, 0, 0))
 
+    def test_calibration_overlay_uses_distinct_zone_colors_and_draws_labels(self) -> None:
+        frame = Frame(width=40, height=20, rgb=b"\x00\x00\x00" * 800)
+
+        annotated = alarm_snapshots.apply_calibration_overlay(
+            frame,
+            {
+                "zones": [
+                    {
+                        "id": "1",
+                        "label": "区域 1",
+                        "polygon": [[0.05, 0.10], [0.40, 0.10], [0.40, 0.90], [0.05, 0.90]],
+                    },
+                    {
+                        "id": "2",
+                        "label": "区域 2",
+                        "polygon": [[0.55, 0.10], [0.90, 0.10], [0.90, 0.90], [0.55, 0.90]],
+                    },
+                ]
+            },
+        )
+
+        self.assertNotEqual(annotated.pixel(10, 15), annotated.pixel(30, 15))
+        label_pixels = [annotated.pixel(x, y) for y in range(2, 10) for x in range(2, 18)]
+        self.assertTrue(any(max(pixel) >= 220 for pixel in label_pixels), "expected bright label text pixels")
+
+    def test_chinese_label_fallback_uses_readable_ascii_when_font_renderer_is_unavailable(self) -> None:
+        self.assertEqual(fallback_label_text("区域 1"), "R1")
+        self.assertEqual(fallback_label_text("区域 12"), "R12")
+        self.assertEqual(fallback_label_text("垃圾区"), "TRASH")
+
+    def test_docker_image_installs_cjk_fonts_for_alarm_snapshot_labels(self) -> None:
+        dockerfile = (Path(__file__).resolve().parents[1] / "Dockerfile").read_text(encoding="utf-8")
+        self.assertIn("fonts-noto-cjk", dockerfile)
+
     def test_capture_alert_snapshot_encodes_frame_with_configured_calibration_overlay(self) -> None:
         encoded_frames: list[Frame] = []