v0.5.4

This build is about the browser staying up. While a turn ran, the side panel
used to push its whole state — tens of megabytes once transcripts pile up —
through storage and the local bridge every second or two, and the browser
process died right behind one of those pushes. Transcript changes now wait for
the turn to end; settings like the permission mode still land the moment you
change them.

The tab-control card is a list now: one row per page the Agent is working in,
with the page's own Take back, and a Take back all in the header.