fix(frontend): preserve unhandled text directives

[morincl]

Restore literal directive syntax when remark-directive parses ordinary text and no plugin maps the node to HAST.

Background

Fixes #1930.

remark-directive parses colon-prefixed alphabetic text as a textDirective, but unhandled text directives lose their original source during conversion to HAST. This adds a default handler that preserves the source text while retaining the Markdown alert support introduced in #1791.

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Summary by cubic

Preserves literal text when remark-directive parses colon-prefixed words as textDirective, so unhandled directives render as-is instead of being lost. Keeps existing Markdown alerts behavior.

• Bug Fixes
  • Add default textDirective handler in remarkRehypeOptions to emit original source when no HAST mapping is provided.
  • Wire remarkRehypeOptions into react-markdown.
  • Add tests for natural-language colons and full unhandled directive syntax.

^{Written for commit 3fbe32d. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

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