1. File handle leak: SVD_Play_f opened file twice, first handle leaked.
Fix: memset demo state before opening.
2. svdemo_stop now handles both recording and playback via SVD_Stop_f.
Playback stop disconnects client to return to menu.
3. Zombie client timeout: skip SV_CheckTimeouts during playback so
reserved player slots aren't freed.
4. Buffer overflow: increase entity buffer to MAX_GENTITIES*300 and
playerState buffer to MAX_CLIENTS*600 for worst-case first frame.
Made static to avoid stack overflow.
5. svs.time jump: don't overwrite svs.time with recorded time.
Server time advances normally, avoiding timeout/heartbeat issues.
6. map_restart: SVD_ResetDeltaState clears entity/player delta state
so next frame writes full states, preventing corrupt deltas.
7. Demo end and manual stop both disconnect the client.
8. SV_Shutdown cleans up active recording/playback.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>