refactor: move supporters loading to separate API endpoint

- Add SupportersHandler in misc_handlers.py to serve /api/lm/supporters
- Register new endpoint in misc_route_registrar.py
- Remove supporters from page load template context in model_handlers.py
- Create supportersService.js for frontend data fetching
- Update Header.js to fetch supporters when support modal opens
- Modify support_modal.html to use client-side rendering

This change improves page load performance by loading supporters data
on-demand instead of during initial page render.

locales/ja.json

@@ -1342,7 +1342,14 @@
             "showWechatQR": "WeChat QRコードを表示",
             "hideWechatQR": "WeChat QRコードを非表示"
         },
-        "footer": "LoRA Managerをご利用いただきありがとうございます！ ❤️"
+        "footer": "LoRA Managerをご利用いただきありがとうございます！ ❤️",
+        "supporters": {
+            "title": "サポーターの皆様に感謝",
+            "subtitle": "{count} 名のサポーターの皆様に、このプロジェクトを実現していただきありがとうございます",
+            "specialThanks": "特別感謝",
+            "allSupporters": "全サポーター",
+            "totalCount": "サポーター {count} 名"
+        }
     },
     "toast": {
         "general": {