refactor: workspace secrets-core + secrets-mcp MCP SaaS

- Split library (db/crypto/service) and MCP/Web/OAuth binary
- Add deploy examples and CI/docs updates

Made-with: Cursor

crates/secrets-mcp/src/oauth/google.rs

@@ -0,0 +1,66 @@
+use anyhow::{Context, Result};
+use serde::Deserialize;
+
+use super::{OAuthConfig, OAuthUserInfo};
+
+#[derive(Deserialize)]
+struct TokenResponse {
+    access_token: String,
+    #[allow(dead_code)]
+    token_type: String,
+    #[allow(dead_code)]
+    id_token: Option<String>,
+}
+
+#[derive(Deserialize)]
+struct UserInfo {
+    sub: String,
+    email: Option<String>,
+    name: Option<String>,
+    picture: Option<String>,
+}
+
+/// Exchange authorization code for tokens and fetch user profile.
+pub async fn exchange_code(
+    client: &reqwest::Client,
+    config: &OAuthConfig,
+    code: &str,
+) -> Result<OAuthUserInfo> {
+    let token_resp: TokenResponse = client
+        .post("https://oauth2.googleapis.com/token")
+        .form(&[
+            ("code", code),
+            ("client_id", &config.client_id),
+            ("client_secret", &config.client_secret),
+            ("redirect_uri", &config.redirect_uri),
+            ("grant_type", "authorization_code"),
+        ])
+        .send()
+        .await
+        .context("failed to exchange Google code")?
+        .error_for_status()
+        .context("Google token endpoint error")?
+        .json()
+        .await
+        .context("failed to parse Google token response")?;
+
+    let user: UserInfo = client
+        .get("https://openidconnect.googleapis.com/v1/userinfo")
+        .bearer_auth(&token_resp.access_token)
+        .send()
+        .await
+        .context("failed to fetch Google userinfo")?
+        .error_for_status()
+        .context("Google userinfo endpoint error")?
+        .json()
+        .await
+        .context("failed to parse Google userinfo")?;
+
+    Ok(OAuthUserInfo {
+        provider: "google".to_string(),
+        provider_id: user.sub,
+        email: user.email,
+        name: user.name,
+        avatar_url: user.picture,
+    })
+}