[fix] attention_output_gate TP slice when num_kv_heads < TP

[Zhichenzzz]

When num_query_groups < tensor_parallel_size (e.g. num_kv_heads=2, TP=4), query heads are sliced per TP rank in get_query_key_value_tensors but the gate tensor is not, causing gate.view(*x.shape) to fail in _apply_output_gate with a shape mismatch.

Fix: after gate reshape, apply the same TP slice as query when num_query_groups < world_size.

Verified with Qwen3.5-35B-A3B TP=4 CP=2 EP=8 (4 training steps passed, logprob_abs_diff stable at 0.01-0.02).

same as the PR in Miles radixark/miles#972

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[guapisolo]

LGTM on my side. Also ask Yueming for review?