feat: add PWA support with manifest and service worker

client/public/manifest.webmanifest

@@ -0,0 +1,25 @@
+{
+  "name": "Traveling Around The World",
+  "short_name": "Travel Map",
+  "description": "記錄旅程、管理旅遊分類並在地圖上標記足跡的 PWA。",
+  "lang": "zh-Hant",
+  "start_url": "/",
+  "scope": "/",
+  "display": "standalone",
+  "background_color": "#ffffff",
+  "theme_color": "#0f172a",
+  "icons": [
+    {
+      "src": "/icons/icon-192.svg",
+      "sizes": "192x192",
+      "type": "image/svg+xml",
+      "purpose": "any"
+    },
+    {
+      "src": "/icons/icon-512.svg",
+      "sizes": "512x512",
+      "type": "image/svg+xml",
+      "purpose": "any maskable"
+    }
+  ]
+}