docs: add bug bounty security policy draft

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Summary

• Adds a root SECURITY.md for issue H4: Public bug-bounty program #88's public bug-bounty program launch.
• Defines narrow initial scope for the Blend leverage strategy, keeper/loop scripts, deployment scripts, and user-facing unsafe docs.
• Adds draft severity/reward tiers, safe-harbor language, report template, disclosure-pipeline dry-run, and maintainer launch checklist.

Notes

I kept the payout table explicitly non-binding until maintainers publish the final external program URL and funding source. That should avoid accidentally promising rewards before the Immunefi/HackerOne/self-hosted decision is made.

Verification

• git diff --cached --check passed before commit.
• Direct marker inspection passed for the required sections in SECURITY.md.

Refs #88

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I drafted the SECURITY.md bug-bounty policy as a concrete starting point for issue #88.

If TurboLong wants the vendor-ready version, I can do a fixed-scope A$690 launch packet: final scope matrix, severity/reward rubric, disclosure SLA, triage workflow, platform-ready program text, and announcement copy.

Details/proof/payment options: https://0741ec59.farmbot-platform-mvp.pages.dev/hire-agent/

Default payment is USDC on Base or Polygon, or invoice if preferred.