docs(deploy): 更新部署配置和文档

- .env.example: 新增 Gemini OAuth 环境变量配置示例
- config.example.yaml: 新增 Gemini OAuth 配置示例
- README.md: 更新部署文档
- docker-compose.yml: 添加 Gemini OAuth 环境变量传递

deploy/.env.example

@@ -53,3 +53,28 @@ ADMIN_PASSWORD=
 # Leave empty to auto-generate (recommended)
 JWT_SECRET=
 JWT_EXPIRE_HOUR=24
+
+# -----------------------------------------------------------------------------
+# Gemini OAuth (OPTIONAL, required only for Gemini OAuth accounts)
+# -----------------------------------------------------------------------------
+# Sub2API supports TWO Gemini OAuth modes:
+#
+# 1. Code Assist OAuth (需要 GCP project_id)
+#    - Uses: cloudcode-pa.googleapis.com (Code Assist API)
+#    - Auto scopes: cloud-platform + userinfo.email + userinfo.profile
+#    - OAuth Client: Can use built-in Gemini CLI client (留空即可)
+#    - Requires: Google Cloud Platform project with Code Assist enabled
+#
+# 2. AI Studio OAuth (不需要 project_id)
+#    - Uses: generativelanguage.googleapis.com (AI Studio API)
+#    - Default scopes: cloud-platform (+ userinfo.*)
+#    - OAuth Client: Leave empty to use built-in Gemini CLI client; or provide your own.
+#    - Requires: Create OAuth 2.0 Client in GCP Console
+#    - Setup Guide: https://ai.google.dev/gemini-api/docs/oauth
+#
+# Configuration:
+# Use Gemini CLI's public OAuth credentials (same as official Google Gemini CLI tool):
+GEMINI_OAUTH_CLIENT_ID=681255809395-oo8ft2oprdrnp9e3aqf6av3hmdib135j.apps.googleusercontent.com
+GEMINI_OAUTH_CLIENT_SECRET=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
+# Optional; leave empty to auto-select scopes based on oauth_type
+GEMINI_OAUTH_SCOPES=