chore: add fingerprint sweep measurement prototype

[Erilla]

Summary

• add a disposable, redacted live guild-roster fingerprint measurement runner
• record its Ictinus Railway test result and create the threshold-calibration follow-up
• keep the prototype isolated from production worker behavior and persistence

Verification

• pnpm format:check
• pnpm lint
• pnpm typecheck
• pnpm test — 34 files, 214 tests passed
• bounded Railway test measurement — 393 achievement requests, below the 3,000-request cap

Checklist

• This pull request targets main from a short-lived branch.
• The change is focused on one coherent concern.
• Documentation and configuration are updated where needed.
• No credentials, private character data, or local environment files are included.