fix: Fix F821 in pann_features_mlp.py:455: Undefined name CosineAnnealingLR

[exploring-curiosity]

Closes #22

What changed

ruff reports F821 at model_train/old/pann_features_mlp.py:455:

Undefined name CosineAnnealingLR

Fix the cause in model_train/old/pann_features_mlp.py. Change only what this finding requires.

Approach

Add CosineAnnealingLR to the import statement from torch.optim.lr_scheduler in model_train/old/pann_features_mlp.py.
Files: model_train/old/pann_features_mlp.py

Verification

Tier	Result	Detail
T0 Diff sanity	pass	internal: diff sanity
T1 Static	skipped	no notebooks changed
T2 Smoke	skipped	no build step configured
T3 Tests	skipped	pre-existing failure, not introduced by this change
T4 Runtime	skipped	no runtime check configured

Why this is a draft

nothing beyond diff sanity was verified - refusing to merge unverified work

Note: T1 (no notebooks changed), T2 (no build step configured), T3 (pre-existing failure, not introduced by this change), T4 (no runtime check configured) - these were not verified.