feat(auth): 앱(네이티브) 구글 로그인 — @capgo/capacitor-social-login

- 웹은 기존 GIS 유지, Capacitor 네이티브(APK)는 네이티브 구글 로그인 사용
  (웹뷰에서 GIS 팝업/FedCM 미동작 대응)
- 받은 ID 토큰은 기존과 동일하게 백엔드 /api/auth/google 로 검증
- src/lib/googleAuth.ts + LoginPage 네이티브/웹 분기

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package-lock.json

@@ -12,6 +12,7 @@
         "@capacitor/app": "^8.0.0",
         "@capacitor/core": "^8.3.4",
         "@capacitor/geolocation": "^8.2.0",
+        "@capgo/capacitor-social-login": "^8.3.36",
         "@quasar/extras": "^1.16.12",
         "@stomp/stompjs": "^7.3.0",
         "pinia": "^2.3.0",
@@ -187,6 +188,18 @@
       "integrity": "sha512-/C1FUo8/OkKuAT4nCIu/34ny9siNHr9qtFezu4kxm6GY1wNFxrCFWjfYx5C1tUhVGz3fxBABegupkpjXvjCHrw==",
       "license": "ISC"
     },
+    "node_modules/@capgo/capacitor-social-login": {
+      "version": "8.3.36",
+      "resolved": "https://registry.npmjs.org/@capgo/capacitor-social-login/-/capacitor-social-login-8.3.36.tgz",
+      "integrity": "sha512-Y4HYjEJablzbHHwPBrbC2UvHVPsR0bAyCAqBzVBoUEOf0UFHAHyTP3gD9JUTKP/iERU8I+6IA2RWtLqDePCNuA==",
+      "license": "MPL-2.0",
+      "dependencies": {
+        "tslib": "^2.8.1"
+      },
+      "peerDependencies": {
+        "@capacitor/core": ">=8.0.0"
+      }
+    },
     "node_modules/@esbuild/aix-ppc64": {
       "version": "0.25.12",
       "resolved": "https://registry.npmjs.org/@esbuild/aix-ppc64/-/aix-ppc64-0.25.12.tgz",