feat: neutral check run when the snapshot is rejected; operating snapshot refresh

[daichunghy]

What

Closes the improvement candidate recorded in the live-smoke findings (rejected snapshots posted no PatchGate Check Run, leaving only the workflow status):

• When create-check-run: true and the GitHub snapshot is rejected, the Action now posts an idempotent check run with conclusion neutral, titled PatchGate: SNAPSHOT REJECTED, carrying the adapter diagnostic id and remediation. neutral matches the existing evidence_missing mapping — a rejected snapshot is an "could not evaluate" state, not an evaluation verdict.
• If the event payload has no pull-request head SHA, the check run is skipped with a warning instead of guessing a target.
• Evaluation and rejection check runs now share one lookup/update delivery helper, preserving the existing deduplication (update over create) for both.

Also refreshes the AGENTS.md operating snapshot after merges #23 and #25: default branch main@e4052f2, PR ranges #15–#21/#23/#25, latest CI 32563526945 and CodeQL 32563526929, current branch inventory, and the multi-persona review record added to the newest-records line.

Verification

Full npm run verify on this exact tree (rebased onto main@e4052f2): lint, typecheck, budget/pins/events/doc-links/community/dossier checks, audit (0 vulnerabilities), 99 tests including 18 action tests with two new rejection-check-run regressions (neutral conclusion posting and update-over-create), security suite, 25 integration tests, clean rebuild, clean-room verify:dist, consumer fixture, release-candidate check, 5 CLI process tests. Bundle chunks 945/995 replace 113/815; stale chunks removed.

Process notes

• Delivered through the GitHub Git Data API pathway per the recorded Mimosa adjudication (the four transport-tint advisories are false positives on file); no transport code is touched.
• Expected to merge via the recorded administrator decision pattern (enforce_admins lifted temporarily and restored immediately), recorded as a maintainer decision, not independent-review evidence.