Remove keen.json and keen_collections after successful migration

All 103 gems have been successfully migrated to the docs structure:
- 91 organizations across 5 epics
- 4 videos (governance)
- 2 audio (governance, value_scanner)
- 4 books (governance, public_observer)
- 1 article (social_medium)
- 1 document (value_scanner)

Verified by verify_all_gems.py script - all gem IDs confirmed present in docs.
Original keen.json and intermediate collection files no longer needed.

Author: claude