e-footprint-interface

Stage 5 of the spec-driven workflow — archive a shipped feature. Run this only once every task in the feature's tasks.md has shipped AND you are satisfied the work is done (typically after review, and when PR is ready to open). It promotes any durable insight into the live reference specs, then deletes the spec folder. It never writes an archive summary file. Invoke explicitly; it is not auto-chained from feature-implement.