feat(security): whitelist login control + rate limiting + login lockout

[kill-money]

Summary

• Add whitelist_users MongoDB collection with full CRUD interface
• Login RPC enforces whitelist check when whitelistLoginEnabled=1 config is set
• In-memory IP rate limiter (60 req/min) and login failure lockout (5 failures → 5 min lock)
• Admin HTTP routes /whitelist/{add,del,update,search} for managing whitelist entries (direct MongoDB, no gRPC changes)
• Fix Dockerfile: replace pinned go get gomake@v0.0.14 with go mod download to use the version already required by magefile.go

Test plan

• Enable whitelistLoginEnabled=1 in config, verify non-whitelisted users are blocked with error code 20012
• Verify whitelisted users can log in normally
• Verify disabled whitelist entries are blocked
• Trigger 60+ requests/min from same IP and confirm 403 rate-limit response
• Fail login 5 times with same identifier, confirm 5-minute lockout
• Test /whitelist/add, /whitelist/search, /whitelist/update, /whitelist/del admin endpoints
• Rebuild Docker image and confirm mage start succeeds without gomake version errors

🤖 Generated with Claude Code

[github-actions]

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