fix(moq-cli): finalize the avc3 track on stdin EOF

The merge resolution's PublishDecoder::finish() avc3 arm flushed the
Annex-B split and decoded the trailing access unit but never called
import.finish(), so on stdin EOF the H.264 track was never closed. A
downstream subscriber/exporter would hang waiting on the final group
instead of seeing end-of-broadcast. The other arms (fmp4/ts/flv) all
finalize; origin/main's avc3 TrackStream did split-flush + decode-tail +
import.finish(). Restores the missing finish().

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QfH4fCnLu9WHGdAjwW8L3Y

Author: claude

rs/moq-cli/src/publish.rs

@@ -133,6 +133,7 @@ impl PublishDecoder {
 			Self::Avc3 { split, import } => {
 				let tail = split.flush(None)?;
 				import.decode(tail)?;
+				import.finish()?;
 			}
 			Self::Fmp4(d) => d.finish()?,
 			Self::Ts(d) => d.finish()?,