inspect: flush buffered TUI output in the finalizer

For TTY auto-synthesis we buffer dump/verdict output while the alt-screen TUI is active. Fold the buffer flush into the TUI post-run finalizer: it exits the TUI via PostRunComplete, waits for Bubble Tea to tear down, then flushes the buffer.

This preserves the intended output ordering without relying on a later sink to run after the blocking TUI wait, and adds a regression test that the finalizer exits and flushes without hanging.