jotpluggler bugs and improvements

GH outage on the release file server (juggle.py --install times out) forced me to try JP, noting some bugs:

- [ ] doesn't surface LogReader errors (auth or missing logs)
- [ ] doesn't open old routes LogReader/PJ does
- [ ] add dynamic streaming buffer selection like PJ, nice to have
- [ ] dark mode!
- [ ] need to be able to zoom at arbitrary width/height not full height
- [ ] timeline scrubbing to see values of each point, like PJ
- [ ] ability to copy the current time in seconds, like PJ
- [ ] Ctrl+Shift+C to clear all points
- [ ] what is this weird spacing?

- [ ] plotting signal breaks streaming, unclear how to fix

https://github.com/user-attachments/assets/8eef5172-911a-4d18-8df4-e47bbf523daa
- [ ] mouse back button should go back a zoom level

Start by locating jotpluggler and comparing its LogReader/PJ behavior, especially error handling and old routes. Review the attached screenshots and each unchecked item separately; the work is done only when the selected behavior is reproducible, specified, and verified without breaking streaming or plotting.

Written by the indexing model from the issue text.