Delete HtmlCss rather than deprecating it

[HarryCordewener]

Removes HtmlCss from MarkupString.Html. Use AnsiCss.Fixed — the rules are byte-identical.

Why

Every ms-* class — ms-bold, ms-faint, ms-italic, ms-underline, ms-strike, ms-overline, ms-blink, ms-invert, ms-cmd-link — is written by MarkupString.Ansi's AnsiHtmlEmitter. MarkupString.Html writes none of them; it emits the tag it was handed. Someone rendering HTML from MarkupString + MarkupString.Ansi therefore got classes with no rules anywhere in their dependency graph, and no reason to guess the fix lived in a package about raw tags. AnsiCss.Fixed (added in 2c29bfc) puts the sheet where the classes come from.

HtmlCss was left behind as an [Obsolete] forwarder. That was the wrong instinct: a deprecation buys a migration window for consumers you cannot reach, and this library is a day old with one consumer. All it bought was two public names for the same string and a member to carry forever.

Ships as v1.1.0, with 1.0.0 unlisted

Removing public API from a published version is a break, so strictly this wants a major. It ships as a minor instead because 1.0.0 went out the same day and nothing consumes it — unlist 1.0.0 on nuget.org before tagging, which turns "no one is broken" from an assumption into a fact. A pinned exact version still restores; nothing new resolves to it.

PublicAPI.Unshipped.txt records both symbols as *REMOVED*, so the removal is reviewed rather than merely permitted. PackageValidationBaselineVersion comes off for this build — the surface being removed from is the surface it would validate against — and goes back to 1.1.0 once that is published; docs/releasing.md carries both halves.

Verified

• Build clean, 463 tests pass (including the two new guards that hold AnsiCss.Fixed and the emitter together in both directions: every class the emitter can write has a rule, and every rule is for a class it can write).
• dotnet pack clean on all three packages.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

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Run ID: da2682e0-8bb8-4101-8758-0a54ecf7711e

📥 Commits

Reviewing files that changed from the base of the PR and between b0ed2e7 and 493d4e4.

📒 Files selected for processing (8)

• CHANGELOG.md
• MarkupString.Ansi/MarkupString.Ansi.csproj
• MarkupString.Html/HtmlCss.cs
• MarkupString.Html/MarkupString.Html.csproj
• MarkupString.Html/PublicAPI.Shipped.txt
• MarkupString.Html/PublicAPI.Unshipped.txt
• MarkupString/MarkupString.csproj
• docs/releasing.md

💤 Files with no reviewable changes (2)

• MarkupString.Html/HtmlCss.cs
• MarkupString.Html/PublicAPI.Shipped.txt

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Walkthrough

The change removes the obsolete MarkupString.Html.HtmlCss API, documents AnsiCss.Fixed as the stylesheet source, and updates package-validation baseline instructions for regular and major releases.

Changes

API and release validation

Layer / File(s)	Summary
Remove HtmlCss API CHANGELOG.md, MarkupString.Html/HtmlCss.cs, MarkupString.Html/PublicAPI.*.txt	Removes MarkupString.Html.HtmlCss and its Fixed member. The changelog directs users to AnsiCss.Fixed.
Update package-validation guidance MarkupString.Ansi/MarkupString.Ansi.csproj, MarkupString.Html/MarkupString.Html.csproj, MarkupString/MarkupString.csproj, docs/releasing.md	Documents updating PackageValidationBaselineVersion after each release. Major releases can omit the baseline before establishing the new major-version baseline.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk:⚪ Minimal · up to 493d4

This removes the obsolete HtmlCss API and directs consumers to AnsiCss.Fixed. The breaking change and release guidance are documented, with no current merge-blocking risk identified.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: removing HtmlCss instead of retaining it as a deprecated API.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

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