feat(movement): spacebar charged jump with skill-based height

Hold spacebar to charge (0→1 over 1s), release to jump. Height from
GetJumpHeight formula using Jump skill via PlayerWeenie. Jump physics
use MotionInterpreter.jump() → LeaveGround() → get_leave_ground_velocity().

JumpExtent is returned in MovementResult (non-null when jump fires this
frame) so GameWindow can log and eventually send the server jump packet.
Double-jump is prevented by jump_is_allowed() checking Contact+OnWalkable
flags before allowing another jump. Tests updated to use charge-then-release
pattern matching the new input model.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/AcDream.App/Rendering/GameWindow.cs

@@ -1912,6 +1912,13 @@ public sealed class GameWindow : IDisposable
                         forcePositionSequence:  _liveSession.ForcePositionSequence);
                     _liveSession.SendGameAction(body);
                 }
+
+                if (result.JumpExtent.HasValue)
+                {
+                    // TODO: send jump packet to server (format needs research from holtburger).
+                    // Local jump physics work without server acknowledgment for now.
+                    Console.WriteLine($"jump: extent={result.JumpExtent.Value:F2}");
+                }
             }
 
             // Update the player entity's animation cycle to match current motion.