Bump frozen Adobe Acrobat Pro (macOS) to installer-delivered 26.001.21691 (fleetdm#50370)

Automated unfreeze probe, revised after validation. The full unfreeze
failed: the Homebrew cask
reports 26.001.21771 (tracking Adobe's updater manifest), but Adobe's
version-less web installer
DMG still delivers 26.001.21691, so the validator's post-install osquery
check failed at
26.001.21771 — the same installer-lags-manifest behavior that caused the
original freeze.

This PR instead pins the output manifest to 26.001.21691 (the version
the DMG actually installs,
confirmed by the 2026-08-01 validator run) and keeps `"frozen": true` so
the nightly ingester
doesn't bump it back to the cask version.

Frozen since: 2025-12-02 (fleetdm#36609 — "product updated but installer was
not, causing validation issues")
Version: 26.001.21662 -> 26.001.21691 (cask claims 26.001.21771;
installer not updated yet)

Note: the regenerated manifest also picks up a newer
`uninstall_script_ref`, because the frozen
output missed the script-template updates that landed on main while it
was pinned.

Draft until validation reports. Merge only if the FMA checks are green
and the validate shard
actually ran for this slug.

**Related issue:** NA

# Checklist for submitter

- [x] QA'd all new/changed functionality manually — pending CI
validation, see above.

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_Generated by [Claude
Code](https://claude.ai/code/session_01EBxhs5D65LRUwCEJejBLJH)_

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Co-authored-by: allenhouchins <allen@fleetdm.com>

Author: allenhouchins