Replace the modal add/edit form with a master/detail dialog: bookmark
list on the left, the selected bookmark's settings on the right. Edits
are flushed back into the bookmark when the selection changes or the
dialog closes.
Bookmarks gain a "connect on startup" flag (only one at a time, since
the client holds a single connection); MainFrame connects to it once
the window is up.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>