add .op.mdx script format

this would be useful for many reasons:

- adding self-maintenance logic to a markdown file per se
- simply use this as a source code, but reuse the text nodes and process them into structured context/annotations without having to use the `` node as a manual wrapper
- this library can be used: https://github.com/wooorm/markdown-rs
- header-delimited sectiosn (or sth similar) could add "lifecycyle-specific" annotations that only get added when compiling annotation list for a matching lifecycle event

No files or tests are named; start by reviewing the existing parsing and lifecycle-annotation entry points, then evaluate the linked markdown-rs library. Done means .op.mdx files can reuse Markdown text nodes and support lifecycle-specific annotations without requiring manual wrappers.

Written by the indexing model from the issue text.