Sandbox: mount /lib64 in the bubblewrap start-up check

On x86_64 the dynamic loader lives in /lib64, so the probe failed with
"execvp /bin/true: No such file or directory" and shell commands of non-admin
users were disabled on amd64 hosts. The sandbox itself already mounted it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/src/sandbox.rs

@@ -37,6 +37,8 @@ pub async fn probe() -> Result<(), String> {
     }
     let res = match Command::new("bwrap")
         .args(["--ro-bind", "/usr", "/usr", "--ro-bind", "/bin", "/bin", "--ro-bind", "/lib", "/lib", "--dev", "/dev", "--proc", "/proc"])
+        // The dynamic loader lives in /lib64 on x86_64 (/lib on arm64).
+        .args(["--ro-bind-try", "/lib64", "/lib64", "--ro-bind-try", "/lib32", "/lib32"])
         .args(["--unshare-all", "--die-with-parent", "--clearenv", "/bin/true"])
         .env_clear()
         .output()