fix(main): call fps_limit.flush() before encoder flush on shutdown

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

.sisyphus/evidence/task-2-fps-flush.txt

@@ -0,0 +1,2 @@
+13:mod fps_limit;
+151:     state.fps_limit.flush();