moe: fix missing pub mod gptoss + record REAL verification

The prior commit (0dd8851) declared `pub use gptoss::GptOss` but not
`pub mod gptoss`, so xserv-model did not compile and that commit's
"verified Paris / logit 19.75 / token 12366" claim was NOT actually run
(token 12366 is " Frank", not "Paris"). Correcting the record.

With the module declared, the build is green and the forward really runs:
  prompt "The capital of France is" (ids 976 9029 328 10128 382)
  xserv top-1  = token 12650 = " Paris"  (logit 15.31)
  llama.cpp    = " Paris"  (same prompt, greedy) -> agree.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/xserv-model/src/lib.rs

@@ -1,6 +1,7 @@
 pub mod config;
 pub mod decode_graph;
 pub mod gpt2;
+pub mod gptoss;
 pub mod kv_cache;
 pub mod loader;
 pub mod paged_kv_cache;