Replace PTY smoke polling sleeps with event-driven waits

[jmqd]

The PTY smoke harness polls captured output and child exit with fixed sleeps and multi-second deadlines. Under load this adds latency and can flake independently of TUI behavior. Notify the harness on reader output or child exit and wait on that signal with the remaining timeout.

[jmqd]

Context: tests/tui_pty_smoke.rs still has fixed sleep polling around captured output and child exit. This turn removed one unrelated scan-cache regression sleep and verified just check. PTY harness remains a separate test-suite latency/flakiness target.

[jmqd]

Patch: 2135a76 replaces fixed PTY smoke polling sleeps with a Condvar-backed output buffer. Reader threads notify waiters on output and EOF; wait helpers now block on output changes instead of sleeping. Verification: cargo test --features tui-test-support --test tui_pty_smoke passed 6 tests in 1.35s. Full gate: just check passed with 980 tests, clippy, and fmt.

[jmqd]

Additional cleanup: cf6590b removes the remaining sleep loop from the scope-selector panic-poller unit test by using a test-only recv_timeout helper. Focused verification: cargo test scope_selector_status_poller_reports_unavailable_when_status_loader_panics --lib passed. Final full gate at HEAD: just check passed with 980 tests, clippy, and fmt.