[codex] Harden Base Sepolia rehearsal and launch demo

[FlowmemoryAI]

Summary

• adds a Base Sepolia rehearsal path with non-secret plan artifact generation, dry-run/broadcast artifact output, chain-id guard, env docs, read/write smoke templates, source verification notes, and rollback guidance
• hardens live Base Sepolia/Base canary reader behavior with RPC URL validation, bounded scans, atomic state/checkpoint writes, checkpoint resume fields, dashboard feed summaries, and stronger malformed RPC/log handling
• adds the launch demo runbook, dashboard README click path, operator recovery steps, and launch-candidate security boundary review
• expands unsafe-claim scanning across docs and contract boundary docs for production/mainnet/custody/bridge/verifier/hook/audit claims

Verification

• npm run deploy:base-sepolia:plan -- --json
• npm test --prefix services/indexer
• node infra/scripts/check-unsafe-claims.mjs
• npm run contracts:hardening (70 Foundry tests passed; Slither still optional/not on PATH)
• npm test
• npm run launch:candidate
• npm run build --prefix apps/dashboard
• npm run flowchain:full-smoke

Boundaries

This remains V0 local/test plus guarded canary/public testnet rehearsal work. It does not claim production readiness, a production L1, production mainnet deployment, production bridge, production verifier network, audited cryptography, production custody, or production Uniswap v4 hook deployment.