feat: add Hong Kong public holiday support

- Add scripts/fetch_hk.py to fetch HK holidays from 1823.gov.hk
- Make generate_ics() cal_name/cal_desc configurable
- Refactor update.py with REGIONS config; support --region cn|hk flag
- Generate hk/{year}.json and hk/{year}.ics under hk/ subdirectory

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/fetch_hk.py

@@ -0,0 +1,45 @@
+"""Fetch Hong Kong public holiday data from 1823.gov.hk."""
+
+import datetime
+import requests
+
+# Traditional Chinese names, consistent with CN data format
+HK_ICAL_URL = "https://www.1823.gov.hk/common/ical/tc.json"
+
+# Earliest year available from the 1823.gov.hk API
+HK_START_YEAR = 2024
+
+
+def fetch_hk_holiday(year: int) -> dict:
+    """Fetch HK public holidays for a given year.
+
+    HK has no makeup work day (调休) concept, so all entries are isOffDay=True.
+    Data coverage starts from HK_START_YEAR.
+    """
+    response = requests.get(HK_ICAL_URL)
+    response.raise_for_status()
+    data = response.json()
+
+    events = data["vcalendar"][0]["vevent"]
+    days = []
+
+    for event in events:
+        dtstart = event["dtstart"][0]  # "YYYYMMDD"
+        date = datetime.date(int(dtstart[:4]), int(dtstart[4:6]), int(dtstart[6:8]))
+        if date.year != year:
+            continue
+        days.append(
+            {
+                "name": event["summary"],
+                "date": date.isoformat(),
+                "isOffDay": True,
+            }
+        )
+
+    days.sort(key=lambda d: d["date"])
+
+    return {
+        "year": year,
+        "papers": [HK_ICAL_URL],
+        "days": days,
+    }