chore: dedup .github community-health files to canonical root copies (#37)

Removes 4 broken/template-residue community-health duplicates from
`.github/` so GitHub uses the clean canonical **root** versions instead.

| Deleted (broken) | Canonical kept |
|---|---|
| `.github/CONTRIBUTING.md` — wrong clone URL
(`hyperpolymath/standards.git`), malformed, stale names |
`CONTRIBUTING.md` |
| `.github/SECURITY.md` — `{{PGP_FINGERPRINT}}` placeholders |
`SECURITY.md` |
| `.github/CODE_OF_CONDUCT.md` — leftover template-instruction block |
`CODE_OF_CONDUCT.md` |
| `.github/GOVERNANCE.md` — BDFL model, contradicts root |
`GOVERNANCE.adoc` |

Kept `.github/{copilot-instructions.md, pull_request_template.md,
DIRECTORY.adoc}`. No header edits (deletions only).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: hyperpolymath