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>

hk/2026.json

@@ -0,0 +1,95 @@
+{
+    "$schema": "https://raw.githubusercontent.com/NateScarlet/holiday-cn/master/schema.json",
+    "$id": "https://raw.githubusercontent.com/NateScarlet/holiday-cn/master/hk/2026.json",
+    "year": 2026,
+    "papers": [
+        "https://www.1823.gov.hk/common/ical/tc.json"
+    ],
+    "days": [
+        {
+            "name": "一月一日",
+            "date": "2026-01-01",
+            "isOffDay": true
+        },
+        {
+            "name": "農曆年初一",
+            "date": "2026-02-17",
+            "isOffDay": true
+        },
+        {
+            "name": "農曆年初二",
+            "date": "2026-02-18",
+            "isOffDay": true
+        },
+        {
+            "name": "農曆年初三",
+            "date": "2026-02-19",
+            "isOffDay": true
+        },
+        {
+            "name": "耶穌受難節",
+            "date": "2026-04-03",
+            "isOffDay": true
+        },
+        {
+            "name": "耶穌受難節翌日",
+            "date": "2026-04-04",
+            "isOffDay": true
+        },
+        {
+            "name": "清明節翌日",
+            "date": "2026-04-06",
+            "isOffDay": true
+        },
+        {
+            "name": "復活節星期一翌日",
+            "date": "2026-04-07",
+            "isOffDay": true
+        },
+        {
+            "name": "勞動節",
+            "date": "2026-05-01",
+            "isOffDay": true
+        },
+        {
+            "name": "佛誕翌日",
+            "date": "2026-05-25",
+            "isOffDay": true
+        },
+        {
+            "name": "端午節",
+            "date": "2026-06-19",
+            "isOffDay": true
+        },
+        {
+            "name": "香港特別行政區成立紀念日",
+            "date": "2026-07-01",
+            "isOffDay": true
+        },
+        {
+            "name": "中秋節翌日",
+            "date": "2026-09-26",
+            "isOffDay": true
+        },
+        {
+            "name": "國慶日",
+            "date": "2026-10-01",
+            "isOffDay": true
+        },
+        {
+            "name": "重陽節翌日",
+            "date": "2026-10-19",
+            "isOffDay": true
+        },
+        {
+            "name": "聖誕節",
+            "date": "2026-12-25",
+            "isOffDay": true
+        },
+        {
+            "name": "聖誕節後第一個周日",
+            "date": "2026-12-26",
+            "isOffDay": true
+        }
+    ]
+}