content-metadata.md: unwrap HTMLBlock; markdown prose + indented HTML tables

[chrisdp]

Summary

The whole body of content-metadata.md was wrapped in a JSX <HTMLBlock>{...}</HTMLBlock> template literal. ReadMe doesn't run its markdown processor inside HTMLBlock, so the 15 [text](doc:slug) references inside (ContentType → roInt, Rating Attribute Icons, ifHttpAgent, Roku OS 9.3 release notes, content-protection, etc.) rendered literally as bracket-and-parens text.

Changes

Drop the wrapper and rebuild the page so:

• Prose (paragraphs, lists, headings, blockquotes) is plain markdown.
• HTML tables stay HTML — they have nested tables, <br />, <a>, and bullet lists inside cells — but are now indented by nesting depth. Cells that contain a nested matrix table are broken across lines so the inner <table> sits at a reasonable level.
• Standalone <pre><code>...</code></pre> snippets become markdown fenced blocks (and the < / > entities inside them are decoded so they render as <contentType> etc.).
• The Confluence-era hljs syntax-highlighting <span> wrappers are stripped (they would have rendered literally outside HTMLBlock).
• { and } in <td> text are written as JSX template literals ({'{'} / {'}'}) so MDX doesn't read them as JSX expressions; ".parameters[0].body" has its [0] escaped so it isn't read as a reference-style link; <img> tags are self-closed.
• Link styles unified to markdown: <a href="/dev/docs/SLUG"> and [text](/dev/docs/SLUG) become [text](doc:SLUG); same-page <a href="#anchor"> becomes [text](#anchor); external <a href="URL"> with matching text becomes [URL](URL).

Inbound links to #digital-rights-management-drm-control-attributes and #playback-configuration-attributes are preserved because the heading text didn't change.