Unbuckles new arrivals from the seats of the arrival shuttle + a bugfix (#91708)

## About The Pull Request

Makes it so new arrivals automatically unbuckle from the seat when the
arrival shuttle lands on station, this also fixes some logic from #91504
that actually makes the intended "If you're buckled on a shuttle which
has "knockdown" force, you won't be paralyzed - instead, just knocked
down and immobilized for a short period (so you can still use your hands
/ act)." from that PR work
## Why It's Good For The Game

New players should be able to just waddle away from the arrival shuttle
to actually play the game instead of being stuck on their seat trying to
find their seatbelt for 30 minutes (this situation has actually happened
before).
## Changelog
🆑
qol: With Nanotrasen's brand new Auto-Seats™, late crew members will now
automatically unbuckle from their seats when the arrival shuttle arrives
at the destination!
fix: Leaving your seat too early on a shuttle with a knockdown force
will now properly immobilize and knockdown you as intended.
/🆑

code/__DEFINES/dcs/signals/signals_global.dm

@@ -107,3 +107,4 @@
 
 /// Global signal whenever a camera network broadcast is started/stopped/updated: (camera_net, is_show_active, announcement)
 #define COMSIG_GLOB_NETWORK_BROADCAST_UPDATED "!network_broadcast_updated"
+

code/modules/shuttle/mobile_port/shuttle_move_callbacks.dm

@@ -319,19 +319,19 @@ All ShuttleMove procs go here
 		shake_camera(src, shake_force, 1)
 
 /mob/living/lateShuttleMove(turf/oldT, list/movement_force, move_dir)
-	if(buckled)
-		return
-
-	. = ..()
-
 	var/knockdown = movement_force["KNOCKDOWN"]
+	if(buckled && istype(get_area(src), /area/shuttle/arrival))
+		//if we're on the arrival shuttle, unbuckle so that new player's don't get stuck in there
+		buckled.user_unbuckle_mob(src, src)
+		return
 	if(knockdown > 0)
 		if(buckled)
 			// If we're buckled, no stun but we'll still be floored and frozen
 			Knockdown(knockdown)
 			Immobilize(knockdown * 0.5)
-		else
-			Paralyze(knockdown)
+			return
+		Paralyze(knockdown)
+	return ..()
 
 
 /mob/living/simple_animal/hostile/megafauna/onShuttleMove(turf/newT, turf/oldT, list/movement_force, move_dir, obj/docking_port/stationary/old_dock, obj/docking_port/mobile/moving_dock)