When switching agents, the old state/chat streams would block until
data arrived (up to 500ms for statewait, indefinitely for chat).
Now requestStop() closes the fid from the calling thread, which
unblocks the worker's blocking read immediately. This makes agent
switching instant instead of waiting for the read timeout.
Switch streaming reads (chat, state, events) from subprocess-based
ollie-9p to native lib9p via worker threads. This eliminates:
- Process spawn/teardown overhead
- Subprocess failure modes
- Signal handling complexity
Lib9pStreamer uses QThread workers with blocking reads. On stop,
workers are given 200ms to exit cleanly, then abandoned (they'll
exit when the read completes or connection closes).
Also: make KRunner/Kate/KIO plugins optional in CMakeLists.txt
to fix build when KF6Runner etc aren't installed. Added
QT_DEFAULT_MAJOR_VERSION=6 to fix Qt6 detection with CMake 4.x.
Levi Neely