The first interactive submit fired session.generateTitle() before
startPendingSubmission() painted the optimistic user row, and
tinyTitleClient.generate() spawned the local tiny-title subprocess
synchronously in #ensureWorker() before its first await. With a local
providers.tinyModel configured, subprocess-spawn latency therefore landed
ahead of the first frame, stalling the first prompt.
Paint the pending row before starting titling, and prewarm an idle,
unref'd worker at TUI startup via a no-op ping (no model load) so the
first submit reuses a live subprocess.
Fixes#6462
roboomp
3cdb93cd01