fix(announcements): style every markdown element a body can contain

[KruGoL]

The gap

The composer accepts markdown. This renderer styled nine element types (h1–h3, p, ul/ol/li, strong, code, a) and left everything else at browser defaults — which on a dark card means an invisible <hr>, a borderless GFM table, a blockquote indistinguishable from a paragraph, and an <h4> rendering smaller than the body text above it.

The fenced code block was worse than unstyled. One code override applied inline code's pill — background, text-xs, no wrapping — to block code too, inside a <pre> with no styling of its own. A release note's own install command rendered as a pill-backed run that pushed the modal wider than the viewport instead of scrolling inside it. That is precisely the content an SDK announcement is made of:

const providers = createWalletApiProviders(base, { baseUrl, network });

The fix

pre owns the background and the horizontal scroll, and tells code which context it is in through a small context.

Why a context and not the two obvious shortcuts:

• react-markdown v10 dropped the inline prop, and the usual replacement — treat className: language-* as "block" — is wrong: a fence written without a language carries no className and falls back to inline styling. There is a test for exactly that case.
• Descendant CSS (pre code { … }) cannot do it either: the inline pill sets its background through a style attribute, which no class from an ancestor can override.

Also styled: tables (same scroll containment — a version-comparison table outgrows a 512px modal long before it is unreasonable to write), blockquote, hr, h4–h6, del, and images. ![alt](url) is markdown rather than raw HTML, so that element already existed whether or not anyone styled it; it now stays inside the card width, loads lazily, and carries referrerPolicy="no-referrer" so a body's image cannot report the reader's current URL to whatever host it points at.

No rehype-raw, no dangerouslySetInnerHTML — raw HTML in a body stays inert text, and this file's own test now says so rather than relying on the modal's.

Tests

New Markdown.test.tsx, 9 tests; 7 of them verified to fail against main (the two that passed are inline code and the raw-HTML guard, neither of which this PR changes).

vitest run — 180 passed (24 files). npm run build clean. npm run lint is still not runnable in this repo: it has neither eslint nor an eslint config installed.