Markdown or plain-text based editor for documents

When using the visual document editor ("Writing area" on notebook.ai), I stumbled on different issues with this editor (see #883, #884). Also, I find WYSIWYG editors very distracting. It would be great to have an editor that is somehow text based and gives me the control to prevent or circumvent the linked issues.

With a markdown (or similar text-based) editor, the formatting would not rely on hidden things - e.g. in #883 there is no indication where the unremovable headlines come from. With a text based editor I could see a `#` or another headline formatting command.

Currently, markdown is used in the object editor, e.g. https://www.notebook.ai/plan/characters/new and as far as I've tried it covers the basic formatting: headlines, bold, italics, quotes, object links ('[[Group-Key]]`). See the example on https://www.notebook.ai/plan/characters/1038910

I did not find support for alignment, nor links of the form `[text](target)`.

Start with the visual document editor, or “Writing area,” and compare its formatting capabilities with the markdown editor used in the object editor examples linked in the issue. Define the supported text-based formatting, including headings, emphasis, quotes, object links, alignment, and standard links, and verify that document editing uses it without the reported WYSIWYG issues.

Written by the indexing model from the issue text.