Support removing ChatGPT OAuth credentials

The DELETE /api/providers/openai-chatgpt endpoint now removes the
OAuth JSON credentials file instead of trying to look up a TOML key.
Re-enable the Remove button in the UI for the ChatGPT Plus card.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: marijnvdwerf

interface/src/routes/Settings.tsx

@@ -601,10 +601,10 @@ export function Settings() {
 													configured={isConfigured("openai-chatgpt")}
 													defaultModel={CHATGPT_OAUTH_DEFAULT_MODEL}
 													onEdit={() => setOpenAiOAuthDialogOpen(true)}
-													onRemove={() => {}}
-													removing={false}
+													onRemove={() => removeMutation.mutate("openai-chatgpt")}
+													removing={removeMutation.isPending}
 													actionLabel="Sign in"
-													showRemove={false}
+													showRemove={isConfigured("openai-chatgpt")}
 												/>
 											) : null,
 										]

src/api/providers.rs

@@ -958,6 +958,22 @@ pub(super) async fn delete_provider(
     State(state): State<Arc<ApiState>>,
     axum::extract::Path(provider): axum::extract::Path<String>,
 ) -> Result<Json<ProviderUpdateResponse>, StatusCode> {
+    // OpenAI ChatGPT OAuth credentials are stored as a separate JSON file,
+    // not in the TOML config, so handle removal separately.
+    if provider == "openai-chatgpt" {
+        let instance_dir = (**state.instance_dir.load()).clone();
+        let cred_path = crate::openai_auth::credentials_path(&instance_dir);
+        if cred_path.exists() {
+            tokio::fs::remove_file(&cred_path)
+                .await
+                .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;
+        }
+        return Ok(Json(ProviderUpdateResponse {
+            success: true,
+            message: "ChatGPT Plus OAuth credentials removed".into(),
+        }));
+    }
+
     let Some(key_name) = provider_toml_key(&provider) else {
         return Ok(Json(ProviderUpdateResponse {
             success: false,