Prepare release bundle without replacing collected evidence

[mellowcroc]

Summary

• Prepare the bundle inside the existing operational evidence directory without replacing receipts.
• Require the exact release path; reject output collisions and symlinked directories. Preserve interrupted output for inspection.
• Evidence verification, signatures, release gates, and other signing-export behavior are unchanged.

Validation

• All PR CI jobs passed, including real Groth16 ownership round-trips and reproducible unsigned rehearsal.
• Linux AMD64 CLI/internal ceremony suites and CLI vet passed under 2 CPU / 2 GiB limits.
• Export concurrency/collision tests passed with the race detector (10 repetitions).
• Published as mpc-ci-1405da9e1830dcb19faa1b0ba42a0935d9c095d7; downstream Relay Harden mainnet ceremony and browser proof recovery Anastasia-Labs/proof-tool#34 and its released three-image tiny ceremony passed through bundle preparation/signing and final release verification.
• No wallet flow, production keys, or proof profiles change. Local pnpm test:all and the live Preprod claim lane were not run.