Problem: SystemStackError: stack level too deep occurred when rendering
messages with indented content (4+ spaces) for WhatsApp, Instagram, and
Facebook channels.
Root Cause: CommonMarker::Renderer#code_block contains a self-recursive
placeholder that must be overridden:
```
def code_block(node)
code_block(node) # calls itself infinitely
end
```
WhatsAppRenderer and InstagramRenderer were missing this override,
causing infinite recursion when markdown with 4-space indentation
(interpreted as code blocks) was rendered.
Fix: Added code_block method to both renderers that outputs the node
content as plain text:
```
def code_block(node)
out(node.string_content)
end
```
Fix https://linear.app/chatwoot/issue/CW-6217/systemstackerror-stack-level-too-deep-systemstackerror
79381a4c5f