fix(anim): stop ACE echo from clobbering player's speedMod; synthesize sequencer velocity

Two related bugs in the motion/animation pipeline:

1. Player's local animation was getting reset to speedMod=1.0 every ~100ms.
   ACE's BroadcastMovement echoes the player's own motion back via
   UpdateMotion. When ACE's ForwardSpeed == 1.0, the ForwardSpeed flag is
   omitted (InterpretedMotionState.BuildMovementFlags), so our wire parser
   returns null and we default to speedMod=1.0 — clobbering the
   locally-authoritative 2.375 × runRate that UpdatePlayerAnimation just
   set. Legs would crank up to full cadence for one frame then get slammed
   back to walking rate.

   Fix: for the player's own guid, skip the wire-echo SetCycle entirely.
   UpdatePlayerAnimation is the authoritative driver for the local
   player's animation; the server echo is only useful for observers of
   other characters. User-confirmed: legs now hold their full cadence.

2. Remote entities teleported between UpdatePositions because the
   sequencer's CurrentVelocity was always zero (Humanoid dat ships every
   locomotion MotionData with Flags=0x00, so EnqueueMotionData leaves
   CurrentVelocity at Vector3.Zero). Dead-reckoning's Priority 1
   (sequencer velocity) never triggered, falling through to EMA which
   has bootstrap lag + gets polluted by teleport-class server snaps.

   Fix: synthesize CurrentVelocity in SetCycle from the retail locomotion
   constants (WalkAnimSpeed=3.12, RunAnimSpeed=4.0, SidestepAnimSpeed=1.25)
   × speedMod, matching the decompiled get_state_velocity (FUN_00528960)
   which uses these same constants directly instead of MotionData.Velocity.
   The dat's HasVelocity field is reserved for non-locomotion motions
   (kick-off velocities, flying creatures, etc).

   Diag confirmed synthesis fires and DR picks it up with src=seq and
   correct magnitude. More visual polish may still be needed for the
   "lagging remote" symptom — see follow-up.

Also adds `PlayerMovementController.BodyVelocity` utility getter for HUD/
debug use, and `ACDREAM_ANIM_SPEED_SCALE` env var as a tunable knob for
visual pacing overrides.

All 717 tests green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.App/Input/PlayerMovementController.cs

@@ -117,6 +117,9 @@ public sealed class PlayerMovementController
     /// </summary>
     public float VerticalVelocity => _body.Velocity.Z;
 
+    /// <summary>Full 3D world-space velocity of the physics body. Exposed for diagnostic logging.</summary>
+    public Vector3 BodyVelocity => _body.Velocity;
+
     // Jump charge state.
     private bool _jumpCharging;
     private float _jumpExtent;