Function channel_streaming_matrix 

pub fn channel_streaming_matrix(root: &Value) -> String

Build the channel streaming-capability table by walking the channels section of the Config schema. Capability is derived from each channel struct’s fields, never hand-listed:

• has stream_mode (the off/partial/multi_message enum) -> draft updates and multi-message streaming are both supported.
• has stream_drafts (a partial-only boolean) -> draft updates only.
• neither -> no streaming.

Returns a Markdown table sorted by channel key.