feat(cnn_v3): patch alignment search, resume, Ctrl-C save

- --patch-search-window N: at dataset init, find per-patch (dx,dy) in
  [-N,N]² that minimises grayscale MSE between source albedo and target;
  result cached so __getitem__ pays only a list-lookup per sample.
- --resume [CKPT]: restore model + Adam state from a checkpoint; omit
  path to auto-select the latest in --checkpoint-dir.
- Ctrl-C (SIGINT) finishes the current batch, then saves a checkpoint
  before exiting; finally-block guarded so no spurious epoch-0 save.
- Review: remove unused sd variable, lift patch_idx out of duplicate
  computation, move _LUMA to Constants block, update module docstring.

handoff(Gemini): cnn_v3/training updated — no C++ or test changes.

0 files changed, 0 insertions, 0 deletions