Streaming UI improvements

[willcrichton]

1. Allow copying text out of screen (marking as WONTFIX since seems hard to support this in blessed. alt-click works on iterm)
2. Figure out how to clear screen on process watch re-run-
3. Show an icon on the bottom button when a critical process is failing
4. Keyboard shortcut (tab?) for changing tabs

[willcrichton]

Items 2 and 3 are tricky, since we would need watched processes to raise some kind of readable signal during watch. One option would be to print compiler-legible output, postprocess within Graco, then log back as human-readable. That's doable for esbuild, but doesn't seem straightforward for TS: microsoft/TypeScript#31566