fix: show oauth url and code properly on device auth popup

- Auth flow now waits for user's Enter before starting
- Start auth only when user presses Enter on DeviceAuth popup
- Proper error handling: missing GOOGLE_CLIENT_ID shows clear message
- Error messages displayed in popup with Retry option
- Popup shows instructions before auth, URL+code during auth
- Handle both verification_url and verification_uri field names from Google
- Check HTTP status code and show error_description on failures
- AuthError propagated to render function for display
- Popup border turns green when URL+code are ready

src/infrastructure/api.rs

@@ -70,6 +70,12 @@ impl ApiClient {
     }
 
     pub async fn authenticate(&self) -> Result<(String, String), ApiError> {
+        if self.client_id.is_empty() {
+            return Err(ApiError::Auth(
+                "GOOGLE_CLIENT_ID not set".to_string(),
+            ));
+        }
+
         let params = serde_json::json!({
             "client_id": self.client_id,
             "scope": "https://www.googleapis.com/auth/tasks",
@@ -81,16 +87,26 @@ impl ApiClient {
             .json(&params)
             .send()
             .await
-            .map_err(|e| ApiError::Network(e.to_string()))?;
+            .map_err(|e| ApiError::Network(format!("HTTP request failed: {}", e)))?;
 
+        let status = resp.status();
         let data: serde_json::Value = resp
             .json()
             .await
-            .map_err(|e| ApiError::Network(e.to_string()))?;
+            .map_err(|e| ApiError::Api(format!("Invalid response (status {}): {}", status, e)))?;
+
+        if !status.is_success() {
+            let err_desc = data["error_description"]
+                .as_str()
+                .or_else(|| data["error"].as_str())
+                .unwrap_or("unknown error");
+            return Err(ApiError::Api(format!("OAuth error ({}): {}", status, err_desc)));
+        }
 
         let url = data["verification_url"]
             .as_str()
-            .unwrap_or(&data["verification_url"].to_string())
+            .or_else(|| data["verification_uri"].as_str())
+            .unwrap_or("https://www.google.com/device")
             .to_string();
         let code = data["user_code"]
             .as_str()