Document mechanical preflight while preserving submission cooldowns

[dcposch]

Companion to PalomarSubmission #130.

Summary

Agents need instructions for running the reusable mechanical verifier before submitting. Add a concise Mechanical preflight section to llms.txt: use mode: full, pin the workflow and pipeline_commit to the same commit, inspect the report, and address resource failures before retrying. Explain that preflight is advisory and excludes Challenge rendering, editorial review, and registration.

Preserve the existing exponential backoff, including after verification-error, and document cooldowns as inference/CI cost controls. Add a regression test confirming that polling a verification error preserves the complete rate record and does not reset the cooldown.

The resource profile is workflow/report metadata, so no Comparator schema extension is needed. Retain the dependency-audit fixes already in this PR: Vitest 4.1.11, js-yaml 4.3.2, and Miniflare's Sharp override at 0.35.4.

Validation

One commit on current server main (341a610). Local checks pass:

• ESLint; 370 Node tests; 9 Worker runtime tests.
• Full dependency audit: zero vulnerabilities.
• Dashboard backward compatibility.
• Formalization/browser preflight contract against current PalomarSubmission main (a013555).

The documented reusable workflow is introduced by PalomarSubmission #130; merge that companion before publishing these instructions. The server contract check now passes independently of that merge.

[dcposch]

cc @kim-em , looks like tests pass except the contract test

that one depends on PalomarRegistry/PalomarSubmission#130 & should pass once that's merged

[kim-em]

Sorry, I don't think I want to do the refund. I'm very happy to improve documentation, but the cooldown is not a penalty, it is making sure our inference/CI costs don't explode, and so who is "at fault" doesn't really matter.

[dcposch]

@kim-em makes sense. I've updated it to just the preflight instructions, lmk if that looks right