v5d: save best-epoch checkpoint during SFT

v5c: add --min-investigation-steps filter for submit-only with longer contexts

v5b: add --submit-only SFT mode

v5: remove 4-bit quant, variable-length traces, submit oversampling, GRPO exploration fixes

Upload folder using huggingface_hub

Fix Qwen3 thinking mode + increase max_new_tokens: training/train_sft.py

Add InvoiceGuard SFT and merge tooling