docs(readme): add Modal training-compute sub-bullet linking the training script

docs(readme): add X social post link under Links

docs(readme): link shared agent-trace dataset in Links

Update README.md

README: note Modal training (sponsor prize, development arm)

README: describe the single journal product (drop legacy surface mention)

README: submission links, track/badge tags, and accurate fine-tune model description

Initial commit: Kintsugi Garden — Build Small Hackathon submission