MarkdownViewer article and demos

[laurenic0l]

Here's the first draft of the MarkdownViewer documentation. POM file should be updated with 25.11

closes #659

[hyyan]

@laurenic0l This article has a few issues. The flow is not completely smooth, and it makes some incorrect assumptions.

1. Conflates "streaming" with "progressive rendering"

   • append() works independently - content appears immediately if progressiveRender is off
   • "Streaming methods" section title is misleading
   • Streaming is about receiving data from server
   • Progressive rendering is about displaying it character-by-character

2. Missing dependency clarity

   • isRendering() only meaningful when progressiveRender is enabled
   • stop(), flush(), whenRenderComplete() only work with progressiveRender on
   • These dependencies aren't explained

3. Auto-scroll placement

   • Presented as if related to streaming, but it's completely independent
   • Can be used with or without streaming/progressive rendering

4. Organization implies wrong flow

   • Suggests you need "streaming methods" for progressive rendering
   • Reality: you can append() without progressiveRender

I suggest this structure, please verify:

1. Setting content
2. Appending content (for any incremental updates)
3. Auto-scroll (independent feature)
4. Progressive rendering (visual typewriter effect)
   • Enable it
   • Render speed
   • Render state (isRendering)
   • Controlling rendering (stop/flush)
   • Waiting for completion (whenRenderComplete)
5. Clearing content
6. Syntax highlighting