Render live transcript of current channels

[reefdog]

A live transcript feed of the currently-selected channels (one box for each channel):

• Render sentences similar to entity detail box (same color, time stamping, etc.) but with channel tag instead of "header"
• Stream new sentences in (and keep some long recent history for scrolling back)
• Keep transcript scroll view "locked" to bottom/latest transcript items (until we manually scroll back)
• Add animated typing indicator in footer
• When we scroll back, lazy-load older transcript items as necessary with fetchMore
• When we scroll back, replace animated indicator with "jump to most recent transcript" link (until we click it or scroll back to most recent transcript items)
• Expand/collapse toggle button in footer increases/decreases transcript height
• Hide expand/collapse button when entity detail box is open
• Hide expand/collapse button if there's no overflow sentences
• Entities in transcript appear as links and behave like entities in list and graph: hovering highlights them in list/graph and clicking opens their detail box