chore: remove stale dated session notes (2026-01-30)

Removes 6 session-summary files dated 2026-01-30 (older than the
2026-04-21 staleness cutoff) describing completed work, plus the
README.md.old backup in rhodium-standard-repositories/examples/.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath