fix(browser): use correct env var for --no-sandbox bypass

AGENT_BROWSER_CHROME_FLAGS is not read by agent-browser CLI.
The correct env var is AGENT_BROWSER_ARGS, with comma-separated values.

This fixes Chrome 'No usable sandbox' crash on Ubuntu 23.10+ systems
where AppArmor restricts unprivileged user namespaces. The detection
logic was correct but the fix used the wrong environment variable name
and space-separated instead of comma-separated args.

tools/browser_tool.py

@@ -1892,8 +1892,8 @@ def _run_browser_command(
                 except OSError:
                     pass
             if _needs_sandbox_bypass:
-                browser_env["AGENT_BROWSER_CHROME_FLAGS"] = (
-                    "--no-sandbox --disable-dev-shm-usage"
+                browser_env["AGENT_BROWSER_ARGS"] = (
+                    "--no-sandbox,--disable-dev-shm-usage"
                 )
 
         # Use temp files for stdout/stderr instead of pipes.