fix(cli): ignore stale slug history in missing redirects check

[kafkas]

Description

Linear ticket: Closes FER-9430

Fixes false positives in the missing-redirects check when FDR returns multiple historical slug mappings for the same pageId.

The rule now keeps only the most recent slug-table row per pageId before comparing published state against the local docs config. This makes the check resilient both to stale rows already present in FDR and to future FDR behavior where older mappings may be preserved intentionally for docs-site versioning.

Changes Made

• Added keepLatestEntryPerPageId() to dedupe FDR markdown entries down to the latest slug per page before running redirect validation
• Updated the missing-redirects rule and test suite to cover stale historical rows, changelog-style shared slugs, and real move/remove cases

Testing

• Unit tests added/updated
• Manual testing completed

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