chore(assets): migrate local images to remote storage

- Replace local image paths with remote URLs in components, content, and config.
- Remove local image files from the public directory to reduce repository size.
- Add dark mode support for the hero background image in `index.vue`.

content/events/20250927-return-to-school.md

@@ -3,16 +3,16 @@ title: "927 永中 • 钟意你"
 subtitle: "永中校友会 39周年庆" 
 date: "2025-09-27"
 location: "永平中学校园"
-cover: "/events/20250927-return-to-school/event-photo-1.jpg"
+cover: "https://img.yphsalumni.org/i/2025/11/28/qr1l7k.jpg"
 ---
 # 永中校友会39周年会庆午宴 温馨欢聚350人
 
-![来宾打卡照](/events/20250927-return-to-school/event-photo-1.jpg)
+![来宾打卡照](https://img.yphsalumni.org/i/2025/11/28/qr1l7k.jpg)
 来宾打卡照（星洲日报记者，邹智敏摄）
 
 永平中学校友会于 9 月 27 日举办“927 永中·钟意你”39 周年会庆午宴，吸引约 350 位校友与社会贤达齐聚一堂，共度温馨时光，场面热闹盛大。
 
-![嘉宾合照](/events/20250927-return-to-school/event-photo-2.jpg)
+![嘉宾合照](https://img.yphsalumni.org/i/2025/11/28/qr1rrx.jpg)
 与会嘉宾向永中校友会献上祝福，左起：许敏捷、王飞兴、林添顺、李煜斌、刘镇东、蓝宜宏、傅庆隆、张嘉群及郑凯聪（星洲日报记者，邹智敏摄）
 
 本次会庆出席嘉宾包括：

content/events/20251009-roulian-xiaoyouhui-20th.md

@@ -3,11 +3,11 @@ title: "柔联校友会 20 届理事就职典礼"
 subtitle: "中学生写作比赛颁奖" 
 date: "2025-10-09"
 location: "富华冷气酒家 2 楼"
-cover: "/events/20251009-roulian-xiaoyouhui-20th/event-photo-1.jpg"
+cover: "https://img.yphsalumni.org/i/2025/11/28/qryfft.jpg"
 ---
 # 柔联校友会 20 届理事就职典礼
 
-![新届理事合照](/events/20251009-roulian-xiaoyouhui-20th/event-photo-1.jpg)
+![新届理事合照](https://img.yphsalumni.org/i/2025/11/28/qryfft.jpg)
 
 柔佛州华校校友联合会日前举办第 20 届理事就职典礼与 2025 年 “林赛花教育基金” 柔佛州中学生现场写作比赛颁奖典礼，由马来西亚华校校友会联合总会会长萧成兴担任监誓人。