physics: sync camera pitch to movement packets and mount tilt during flight

- Add setMovementPitch() and isSwimming() to GameHandler
- In the per-frame sync block, derive the pitch angle from the camera's
  forward vector (asin of the Z component) and write it to movementInfo.pitch
  whenever FLYING or SWIMMING flags are set — the server includes the pitch
  field in those packets, so sending 0 made other players see the character
  flying perfectly flat even when the camera was pitched
- Also tilt the mount model (setMountPitchRoll) to match the flight direction
  during player-controlled flight, and reset to 0 when not flying

include/game/game_handler.hpp

@@ -1179,6 +1179,12 @@ public:
     bool isHovering() const {
         return (movementInfo.flags & static_cast<uint32_t>(MovementFlags::HOVER)) != 0;
     }
+    bool isSwimming() const {
+        return (movementInfo.flags & static_cast<uint32_t>(MovementFlags::SWIMMING)) != 0;
+    }
+    // Set the character pitch angle (radians) for movement packets (flight / swimming).
+    // Positive = nose up, negative = nose down.
+    void setMovementPitch(float radians) { movementInfo.pitch = radians; }
     void dismount();
 
     // Taxi / Flight Paths