feat: 구글 로그인/가입 — 웹(GIS)·앱(네이티브 Credential Manager)

- LoginModal: 서버에서 구글 클라이언트 ID 수신 시에만 버튼 노출
  - 웹/PC: Google Identity Services 렌더 버튼
  - 앱(안드로이드): @capawesome/capacitor-google-sign-in 네이티브 버튼
- 네이티브/웹 모두 ID 토큰을 /api/auth/google 로 전달(aud=웹 클라이언트 ID)
- auth 스토어/authApi 에 googleLogin·googleClientId 추가
- src/native/googleAuth.js 네이티브 래퍼 신규

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

android/app/capacitor.build.gradle

@@ -12,6 +12,7 @@ dependencies {
     implementation project(':capacitor-app')
     implementation project(':capacitor-camera')
     implementation project(':capacitor-preferences')
+    implementation project(':capawesome-capacitor-google-sign-in')
 
 }
 

android/capacitor.settings.gradle

@@ -10,3 +10,6 @@ project(':capacitor-camera').projectDir = new File('../node_modules/@capacitor/c
 
 include ':capacitor-preferences'
 project(':capacitor-preferences').projectDir = new File('../node_modules/@capacitor/preferences/android')
+
+include ':capawesome-capacitor-google-sign-in'
+project(':capawesome-capacitor-google-sign-in').projectDir = new File('../node_modules/@capawesome/capacitor-google-sign-in/android')