Add mount pitch and roll for realistic taxi flight animation

Flying mounts now tilt and bank realistically during taxi flights:
- Pitch (up/down): calculated from spline tangent's z-component (altitude change)
- Roll (banking): proportional to turn rate, clamped to ~40 degrees
- Yaw: existing horizontal orientation from spline direction

Implementation:
- Added mountPitch_ and mountRoll_ to Renderer (radians)
- Updated TaxiOrientationCallback to pass yaw, pitch, roll
- Calculate pitch using asin(tangent.z) for altitude tilt
- Calculate roll from yaw change rate: -orientDiff * 2.5, clamped to ±0.7 rad
- Applied to mount rotation: glm::vec3(pitch, roll, yaw)

This fixes the "weirdness" where mounts flew sideways or without natural banking.

src/core/application.cpp

@@ -719,11 +719,13 @@ void Application::setupUICallbacks() {
     });
 
     // Taxi orientation callback - update mount rotation during flight
-    gameHandler->setTaxiOrientationCallback([this](float orientationRadians) {
+    gameHandler->setTaxiOrientationCallback([this](float yaw, float pitch, float roll) {
         if (renderer && renderer->getCameraController()) {
-            // Convert radians to degrees for camera controller
-            float yawDegrees = glm::degrees(orientationRadians);
+            // Convert radians to degrees for camera controller (character facing)
+            float yawDegrees = glm::degrees(yaw);
             renderer->getCameraController()->setFacingYaw(yawDegrees);
+            // Set mount pitch and roll for realistic flight animation
+            renderer->setMountPitchRoll(pitch, roll);
         }
     });