fix: CommonMark fences and quote-aware component tags (0.1.12-alpha)

[Shewart]

Parser fixes found while rewriting the ShellDocs docs site on 0.1.11, plus the 0.1.12-alpha release prep. Merging this and pushing tag v0.1.12-alpha publishes the release.

Fixed

• A fence longer than three backticks that showed a shorter fence broke the rest of the page. The next razor:preview rendered as plain code and tags inside the example became empty placeholders. Fences now follow CommonMark: three or more backticks or tildes, closed by a run of the same character at least as long. Empty fences and trailing spaces are handled.
• A > inside a quoted attribute value ended an inline component tag early, so the component silently disappeared. Inline tags are now read with RazorTagScanner, as razor:preview already was.
• The same problem in named-slot tags (<Icon title="a > b">), which leaked the rest of the tag into the slot.
• Code spans in an attribute value could split the value when the span contained a quote.
• <TypeTable> dropped rows that shared a Name.

Added

• Tilde fences (~~~), including ~~~razor:preview.

Changed

• An inline tag with an unterminated quote, or one that spans a blank line, is passed through as raw markup.
• ShellDocs.Markdown exposes its internals to ShellDocs.Components, so both use the one tag scanner.

Release

• <Version> is 0.1.12-alpha; the CHANGELOG has the dated section and link; ROADMAP is updated.

Verification

• Each of the five commits builds and passes on its own; 322 tests at the tip, 16 of them new. The tests for the bugs fail on main.
• Release build has 0 warnings; the pack dry-run produces the six packages at 0.1.12-alpha; that version is not on nuget.org.
• A/B render of 320 real pages (ShellUI docs, ShellDocs docs, the example site, ShellIcons docs) on main and on this branch: output is identical for every page, so existing content is unaffected.

After merging

git checkout main && git pull
git tag v0.1.12-alpha
git push origin v0.1.12-alpha

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