docs: label historical release ledgers

[codeforester]

Summary

• explicitly mark the v2.0.0 cutover, reference-app evidence, and integration pins as historical baselines
• add reconciliation/review dates and the current v2.1.0 compatibility-canary snapshot
• replace the stale package-channel post-GA wording with the remaining maintained-update-path gate

Validation

• git diff --check
• tests/integration-release-contract.sh
• tests/reference-release-contract.sh
• scripts/first-party-cutover check
• bats tests/first-party-cutover.bats tests/integrations.bats

Fixes #554

[codeforester]

Review at the current head: the historical-record labelling is clear and CI is green, but one item should be fixed before merge.

Needs changes

1. Checked checklist items that the record doesn't support. docs/discovery/awesome-bash.md now marks [x] v2.0.0 release URL and SHA-256 added to this record, but the file contains no release URL or SHA-256. The next two boxes (links resolve without credentials; reference-app and benchmark links resolve) are also ticked without evidence in the PR. Either add the URL and checksum to the record and say how the links were verified, or leave those boxes unchecked.

Non-blocking
2. Review dates are hardcoded into the checks. scripts/first-party-cutover (last_reconciled: 2026-10-07) and the contract tests (last_reviewed: 2026-10-07) now fail unless the date is exactly that value, so every future review has to edit the checks as well as the data. Prefer asserting that the key exists and is a valid YYYY-MM-DD date.
3. Formatting churn. scripts/first-party-cutover was reformatted wholesale, which hides the real change. If the reformat is wanted, a separate commit or PR would make this diff reviewable.

Verified: the 2026-10-05 canary run cited in consumer-validation-status.md (#37327900680) exists, was a scheduled run, and passed all four candidate jobs.

#560 is stacked on this PR and cannot merge until it does.

[codeforester]

Addressed the follow-up review:\n\n- The Awesome Bash checklist no longer claims release URLs, checksums, or link verification that are not recorded in that file; those items are left unchecked.\n- Cutover and release-evidence checks now validate review-date shape as YYYY-MM-DD instead of hardcoding 2026-10-07.\n\nFocused validation passes: docs, integration-release, reference-release, first-party-cutover, BATS, shfmt, and diff checks.

[codeforester]

Follow-up review: both requested fixes are in. The Awesome Bash checklist boxes are unchecked again with accurate wording, and the review-date checks now validate YYYY-MM-DD shape instead of a fixed value. No blockers; CI was still running on the Validate jobs when I checked. One optional nit remains:

• Formatting churn in scripts/first-party-cutover. The whole file is still reformatted, which hides the real change (the new record-scope and date checks). Not worth blocking on, but a separate commit or PR for the reformat would make the history easier to review.

Merge order: this PR first (it is retargeted to main and already contains the merged #560 changelog entries), then #561.

[codeforester]

The formatting nit is already isolated in its own commit (34fff3a, “style: format cutover contract script”), separate from the documentation/evidence changes. I left that reviewable history intact; no further source change is needed.