When an uncaught exception fires in interactive mode, the process dies with
stdin still in raw mode and the cursor hidden, leaving the user with a
"borked" terminal that needs `stty sane && reset` to recover. The most
common trigger is an extension's async ChildProcess `exit` callback that
throws (e.g. from accessing a stale ctx after session replacement), but
this affects any uncaught throw from anywhere in pi.
Add an uncaughtException handler in registerSignalHandlers that calls
ui.stop() before exiting, mirroring the existing emergencyTerminalExit
pattern. The handler is registered with prependListener and tracked in
signalCleanupHandlers, so it is removed on graceful shutdown the same way
the other handlers are.
Unlike emergencyTerminalExit (used for SIGHUP / dead-terminal EIO), the
terminal is still alive on uncaughtException, so we run the normal
ui.stop() to restore cooked mode, the cursor, bracketed paste mode, and
Kitty / modifyOtherKeys sequences.
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