chore(repo): remove leaked internal doc from public repo (#163)

Remove resources/research brief.md which is an internal Ontic Systems
document that should not be in the public repository. The .gitignore
already blocks this path; this commit removes the tracked file.

Follows up on GRA-74 and prior cleanup commits that removed AGENTS.md,
CLAUDE.md, ONTIC_SYSTEMS_INITIALIZATION_BRIEF.md, docs/4.17.26-gradientResearch.md,
and resources/phase3_*.md.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: graydeon