chore(footnote): keep IT-923 analyzer and plan doc local-only (SD-2656)

Untracks tools/sd-2656-footnote-analyzer/ and
docs/architecture/sd-2656-it923-footnote-word-fidelity-plan.md so the
PR diff no longer includes the local diagnostic toolkit or the working
plan document. The files remain on disk for local use.

To re-introduce them later, decide whether each one should be committed
intentionally (review the contents first) or stay outside the repo via
a local gitignore entry.

Author: tupizz