chore(ui-tooling): drop the changeset polarity census's test and fixture corpus (slice 4 of #25920) (#26098)

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_Requested by **Elon** · [project
thread](https://claude.ai/code/project/chan_01WedDzV26nniwxv7jC88B9D?thread=cmsg_01WedDzV26nniwxv7jC88B9D7sHdFfY8QjwRsxKSLngGfv)_

Part of #25920 — slice 4 of the unwired-tooling cleanup (slices 1–3:
#26004, #26024, #26057). The card stays open.

## Summary

Deletions only: 17 files, −1,654 lines, on `main` b63fdf7.

- `ui/scripts/__tests__/changeset-polarity-census.test.ts` + its fixture
corpus `ui/scripts/__tests__/fixtures/changeset-polarity/` → **delete.**
They pin `changeset-polarity-census.mjs`, the instrument for
objectui#9727, which closed after the rebuild. No gate, workflow or
document runs the census or its test.
- `ui/scripts/markdown-test-inputs.mjs`: the test's row (and its
comment) goes with it, so the markdown-input inventory stays exact.

The census script itself and its `census:changeset-polarity` alias
(−1,882) follow in the next slice: the two together would cross the
3,000-line single-PR threshold.

## Verification (head 2c26b8a)

- Exact-name `git grep` across the whole tree for the test and the
fixture path: the only hit left is the census script's own header
comment, which goes in the next slice. Nothing in AGENTS.md, `skills/**`
or `.claude/**` names either.
- ui suites that read the scripts inventory and manifest
(markdown-test-inputs, package-scripts-vitest-projects,
check-unreferenced-sources, vitest-invocation-guard): 4 files, 107 tests
passed. (`ci-cd-pipeline-doc.test.ts`, run on earlier slices, was
retired on `main` by #26058.)
- `check:unreferenced-sources`, `check:test-path-roots`,
`check-ci-filter-parity` and its `--self-test`: exit 0.
`check:commit-card-trailers`: exit 0.
- `dispatch-gates --commands` families: per-family exit codes in the
report on the card.
- No changeset: private ui tooling only.

---
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Co-authored-by: Claude <noreply@anthropic.com>

Author: objectstack-fleet[bot]