MOAD-0003 (Leaked Context): CLEAN

TLS variables in xenia:
  - current_xthread_tls_ (xthread.cc): set at thread start, cleared at exit. 1:1 with thread lifetime.
  - thread_state_ (thread_state.cc): set via ThreadState::Bind(), cleared in destructor. 1:1 with thread.
  - current_thread_ (thread.cc/h): same pattern as above.
  - thread_log_buffer_ (logging.cc): logging scratch buffer, no identity leakage.
  - string_buffer_ (shim_utils.cc): scratch buffer for HLE shims, no identity.

All TLS vars are thread-scoped, not request-scoped. No guest-task identity
leaks across OS-thread reuse found.
