扩展模型区间端点至首尔和釜山，并做前端小幅清理

- GET /api/cities/model-range 新增 seoul/busan，总计 9 城
- 移除未使用的 react-leaflet 依赖
- 提取 chart Tooltip contentStyle 为共享常量 CHART_TOOLTIP_STYLE，消除 6 个文件中 15 处重复内联样式

Tested: npx tsc --noEmit pass
Confidence: high

frontend/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "polyweather-frontend",
-  "version": "1.5.5",
+  "version": "1.7.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "polyweather-frontend",
-      "version": "1.5.5",
+      "version": "1.7.0",
       "dependencies": {
         "@radix-ui/react-slot": "^1.1.2",
         "@supabase/ssr": "^0.5.2",
@@ -20,7 +20,6 @@
         "next": "^15.3.2",
         "react": "^19.0.0",
         "react-dom": "^19.0.0",
-        "react-leaflet": "^5.0.0",
         "recharts": "^3.8.1",
         "tailwind-merge": "^3.3.0"
       },
@@ -362,15 +361,6 @@
         }
       }
     },
-    "node_modules/@react-leaflet/core": {
-      "version": "3.0.0",
-      "license": "Hippocratic-2.1",
-      "peerDependencies": {
-        "leaflet": "^1.9.0",
-        "react": "^19.0.0",
-        "react-dom": "^19.0.0"
-      }
-    },
     "node_modules/@reduxjs/toolkit": {
       "version": "2.12.0",
       "resolved": "https://registry.npmmirror.com/@reduxjs/toolkit/-/toolkit-2.12.0.tgz",
@@ -3302,18 +3292,6 @@
       "license": "MIT",
       "peer": true
     },
-    "node_modules/react-leaflet": {
-      "version": "5.0.0",
-      "license": "Hippocratic-2.1",
-      "dependencies": {
-        "@react-leaflet/core": "^3.0.0"
-      },
-      "peerDependencies": {
-        "leaflet": "^1.9.0",
-        "react": "^19.0.0",
-        "react-dom": "^19.0.0"
-      }
-    },
     "node_modules/react-redux": {
       "version": "9.3.0",
       "resolved": "https://registry.npmmirror.com/react-redux/-/react-redux-9.3.0.tgz",