fix: use correct Browserbase API to release sessions (#707)

Browserbase has no DELETE endpoint for sessions. The correct API is
POST /v1/sessions/:id with body { status: "REQUEST_RELEASE" }. The old
DELETE call returned an error that was silently swallowed, causing every
session to leak until the 30-min idle timeout.

Fixed in both Node.js (src/browser.ts) and native Rust
(cli/src/native/providers.rs) paths.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/browser.ts

@@ -862,12 +862,18 @@ export class BrowserManager {
    * Close a Browserbase session via API
    */
   private async closeBrowserbaseSession(sessionId: string, apiKey: string): Promise<void> {
-    await fetch(`https://api.browserbase.com/v1/sessions/${sessionId}`, {
-      method: 'DELETE',
+    const response = await fetch(`https://api.browserbase.com/v1/sessions/${sessionId}`, {
+      method: 'POST',
       headers: {
+        'Content-Type': 'application/json',
         'X-BB-API-Key': apiKey,
       },
+      body: JSON.stringify({ status: 'REQUEST_RELEASE' }),
     });
+
+    if (!response.ok) {
+      throw new Error(`Failed to close Browserbase session: ${response.statusText}`);
+    }
   }
 
   /**