fix: add --no-sandbox for Chromium in CI/container environments

Chromium's sandbox requires unprivileged user namespaces which are
disabled in Docker containers. Without --no-sandbox, Chromium silently
fails to launch, causing browse E2E tests to exhaust all turns trying
to start the server.

Detects CI or CONTAINER env vars and adds --no-sandbox automatically.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

browse/src/browser-manager.ts

@@ -69,6 +69,13 @@ export class BrowserManager {
     const launchArgs: string[] = [];
     let useHeadless = true;
 
+    // Docker/CI: Chromium sandbox requires unprivileged user namespaces which
+    // are typically disabled in containers. Detect container environment and
+    // add --no-sandbox automatically.
+    if (process.env.CI || process.env.CONTAINER) {
+      launchArgs.push('--no-sandbox');
+    }
+
     if (extensionsDir) {
       launchArgs.push(
         `--disable-extensions-except=${extensionsDir}`,