Demo pause: freeze svs.time, hold demo data consumption

svdemo_pause toggles playback pause. When paused:
- svs.time frozen so entity trajectories freeze correctly
- No demo frames consumed (SVD_PlaybackFrame returns early)
- Game frame still runs at frozen time for spectator movement
- No time jump on unpause — svs.time resumes from where it was

Spectator movement degrades during pause (200ms PmoveSingle cap)
— will be resolved by client-owned camera in a future change.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

code/server/server.h

@@ -353,9 +353,11 @@ void		SVD_CaptureServerCommand( const char *cmd );
 void		SVD_Play_f( void );
 void		SVD_StopPlay_f( void );
 void		SVD_Stop_f( void );
+void		SVD_Pause_f( void );
 qboolean	SVD_PlaybackFrame( void );
 qboolean	SVD_IsRecording( void );
 qboolean	SVD_IsPlaying( void );
+qboolean	SVD_IsPaused( void );
 qboolean	SVD_ShouldPause( void );
 
 //============================================================

code/server/sv_ccmds.c

@@ -744,6 +744,7 @@ void SV_AddOperatorCommands( void ) {
 	Cmd_AddCommand ("svdemo_record", SVD_Record_f);
 	Cmd_AddCommand ("svdemo_stop", SVD_Stop_f);
 	Cmd_AddCommand ("svdemo_play", SVD_Play_f);
+	Cmd_AddCommand ("svdemo_pause", SVD_Pause_f);
 }
 
 /*

code/server/sv_main.c

@@ -831,6 +831,15 @@ void SV_Frame( int msec ) {
 	// run the game simulation in chunks
 	while ( sv.timeResidual >= frameMsec ) {
 		sv.timeResidual -= frameMsec;
+
+		if ( SVD_IsPaused() ) {
+			// demo paused: freeze svs.time so trajectories freeze
+			// and client doesn't see time jumps on unpause.
+			// still run game frame for spectator movement (at frozen time).
+			VM_Call( gvm, GAME_RUN_FRAME, svs.time );
+			continue;
+		}
+
 		svs.time += frameMsec;
 
 		if ( SVD_IsPlaying() ) {