Present a semantic changelog

[hweihwang]

The model from #9047 produces typed descriptors, but a raw list is hard to read and nothing outside Text can use it. This PR turns it into a changelog view and exposes it to other apps.

What's in this PR

• The Changes view: records grouped under the section heading they occurred in, labelled by kind, each with its own before/after preview
• A public factory, window.OCA.Text.createMarkdownContentComparison, so other apps can mount a comparison
• Stable selection by descriptor ID, an explicit "no rendered differences" state, and a hide-formatting-only filter

The Changes view, shown through the Collectives dialog from the integration unit in nextcloud/collectives. Text ships no standalone host, so this is the only way to see the view running today. Text owns the model and views; Collectives owns the dialog.

Design notes

• The changelog is the default view. "What changed" is the usual question.
• The factory is a capability, not a version. Consumers check for the function, not a version string.
• A group of three edits renders three previews. One merged preview lost two of the three.

Stack

Depends on: #9047. Base: review/structured-markdown-comparison-model, retargets to main once #9047 merges. Followed by #9049.

Verification

ts:check and lint pass. The complete suite passes at this tip: 1,820/1,820. Grouping, previews, filters and navigation are exercised by the live end-to-end suite recorded for the Collectives PRs.

Related

• Show differences (added/removed/changed text) when checking past versions collectives#599
• Version difference extraction #4422

Happy to answer any questions in review.

[hweihwang]

Note on CI: the static-psalm-analysis failure is at lib/Migration/Version030201Date20201116110353.php, a 2020 migration this stack does not touch — the diff is limited to src/ and tests. Upstream main's last static-analysis run passed on 2026-08-04; this looks like psalm-version drift flagging an untouched file. Nothing in this PR's diff is involved; happy to look into it upstream if maintainers want a separate fix.