Fix smollm2 alias to point at SmolLM2-135M (v2) instead of SmolLM-135M (v1)

[Copilot]

Summary

The original SmolLM2 PR (#9354) started as v1 support, was renamed to smollm2 during review, but the repo ID and rope_theta were never updated to v2 values. The two checkpoints are genuinely different models (0/272 tensors match).

• HUGGING_FACE_REPO_IDS["smollm2"]: HuggingFaceTB/SmolLM-135M → HuggingFaceTB/SmolLM2-135M
• examples/models/smollm2/135M_config.json: rope_theta 10000.0 → 100000.0 (matches SmolLM2-135M HF config)

Test plan

Data-only change (one string, one number). Verified values match the upstream HuggingFace SmolLM2-135M config.

[pytorch-bot]

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✅ You can merge normally! (2 Unrelated Failures)

As of commit f8eb537 with merge base fe71bd4 ():

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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