fix(desktop): preserve angle brackets in inline code

[ndizazzo]

Summary

• preserve literal angle brackets when the desktop composer serializes Markdown
• replace tiptap-markdown's HTML-escaping text node with a composer-specific serializer
• add regression coverage for inline code, literal HTML entities, and existing Markdown punctuation

The upstream text serializer HTML-escaped < and > before Markdown rendering. Inline code preserves those entity strings literally, so messages such as <repo root>/website displayed as <repo root>/website.

Related issue

N/A — no matching open issue or pull request found.

Testing

• just ci
• focused composer Markdown serialization tests (3 passed)
• full desktop unit suite (4,778 passed)
• desktop TypeScript typecheck
• changed-file Biome check

Manual regression case: type `<repo root>/website` in the desktop composer and send it. The rendered inline code should keep the angle brackets instead of showing HTML entities.

Before: the reported message displayed <repo root>/website.

After: the serializer regression test verifies the emitted Markdown remains `<repo root>/website`.

Original Bug

[micspiral]

nice small one @wesbillman

[Chessing234]

serializeComposerMarkdown does markdown.replace(/\\([*\~[]_])/g, "$1")before returning, so the helper strips exactly the backslash escapes the assertions are about. "Markdown punctuation and inline-code delimiters remain unchanged" therefore passes whether the serializer emittedboldor**bold**` — it cannot fail, and it is the test carrying the claim that this override does not disturb other escaping.

worth asserting on the raw serializer output for that case. the reason it matters: overriding the text node's serializer replaces the stock escaping for every markdown-significant character, not just </>, so *, _, [ and backticks are the ones to pin.

minor, possibly a no-op: state.text(node.text) — prosemirror-markdown's text(text, escape = true) defaults to escaping, so it is not obvious from the diff where the behaviour change comes from. if the fix works by bypassing tiptap-markdown's serializer rather than by that call, that is the thing to say in the comment.