fix VAM: funasr+pyarrow deadlock, librosa+numpy compat, reduce iter_batches batch_size

feat: add VAM SFT mini training (T2A Stage 1)

feat: add VLM SFT mini configs, resume training, dataset streaming, and eval fixes

Add modular development docs under docs/ for learning and interviews

Flatten src layout: drop omni namespace, modules live directly under src/