fix: brain security hardening — PII, IP rate limit, anti-Sybil

[ruvnet]

Summary

• PII redaction expanded (12 → 15 rules): Phone numbers, SSNs, and credit cards now stripped. 555-867-5309 → <PHONE_1>, 078-05-1120 → <SSN_1>, 4111-1111-1111-1111 → <CC_1>
• IP-based rate limiting: Secondary per-IP write limit (1500/hr) prevents Sybil key rotation from a single source
• Anti-Sybil vote dedup: One vote per IP per memory, regardless of API key count. Returns 403 on duplicates

Files Changed

File	Changes
crates/rvf/rvf-federation/src/pii_strip.rs	Add phone, SSN, credit card rules + 7 tests
crates/mcp-brain-server/src/rate_limit.rs	Add IP write/read buckets, IP vote dedup map
crates/mcp-brain-server/src/routes.rs	Add extract_client_ip(), wire IP limits to share/vote
crates/mcp-brain-server/src/verify.rs	Update docs, add phone/SSN/CC tests
docs/adr/ADR-082-*	Full security audit and hardening decisions

Test plan

• 16 PII tests pass (phone, SSN, CC detection + redaction)
• 63 brain server tests pass
• Live verification: phone/SSN/CC redacted in stored content
• Live verification: second vote from different key, same IP → 403
• Deployed to Cloud Run (revision ruvbrain-00076-2jz)

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