v0.5.2

Fixed

Finished sessions no longer sit under "Running" forever on Linux.

On a quiet POSIX pty the busy→idle transition is completed by saikai's
1.5s poll rather than the pane's output reader — and the poll's list
rebuild was deferred for as long as any live pane held focus (the 2s
re-scan was skipped on the same condition). Parking focus in a pane —
the normal working posture, including driving a session from the web
mirror — froze the State groups, so sessions that had finished stayed
grouped under Running until focus returned to the list. Windows never
showed this because ConPTY keeps emitting output after idle, which kept
the reader-side (unconditional) refresh path alive.

Rebuilds are now deferred only while the user is actively typing
into the focused pane (keys, paste, and mirror-injected input all
count), and a deferred rebuild is caught up on the next poll tick
instead of waiting for a focus change.

Verified by a new regression test that drives a real pty child through
busy → idle → total silence with focus parked in the pane
(tests/test_status_regroup.py).