refactor: decompose TransportManager and upgrade Entity to CatmullRom splines

TransportManager decomposition:
- Extract TransportClockSync: server clock offset, yaw flip detection,
  velocity bootstrap, client/server mode switching
- Extract TransportAnimator: spline evaluation, Z clamping, orientation
  from server yaw or spline tangent
- Slim TransportManager to thin orchestrator delegating to ClockSync and
  Animator; add pushTransform() helper to deduplicate WMO/M2 renderer calls
- Remove legacy orientationFromSplineTangent (now uses
  CatmullRomSpline::orientationFromTangent)

Entity path following upgrade:
- Replace pathPoints_/pathSegDists_ linear lerp with
  std::optional<CatmullRomSpline> activeSpline_
- startMoveAlongPath builds SplineKeys with distance-proportional timing
- updateMovement evaluates CatmullRomSpline for smooth Catmull-Rom
  interpolation matching server-side creature movement
- Reset activeSpline_ on setPosition/startMoveTo to prevent stale state

Tests:
- Add test_transport_components (9 cases): ClockSync client/server/reverse
  modes, yaw flip detection, Animator position eval, server yaw, Z clamping
- Link spline.cpp into test_entity for CatmullRomSpline dependency

Signed-off-by: Pavel Okhlopkov <pavel.okhlopkov@flant.com>

include/game/transport_clock_sync.hpp

@@ -0,0 +1,49 @@
+// include/game/transport_clock_sync.hpp
+// Clock synchronization and yaw correction for transports.
+// Extracted from TransportManager (Phase 3a of spline refactoring).
+#pragma once
+
+#include <glm/glm.hpp>
+#include <cstdint>
+
+namespace wowee::math { class CatmullRomSpline; }
+
+namespace wowee::game {
+
+struct ActiveTransport;
+struct PathEntry;
+
+/// Manages clock sync, server-yaw correction, and velocity bootstrap for a single transport.
+class TransportClockSync {
+public:
+    /// Compute pathTimeMs for a transport given current elapsed time and deltaTime.
+    /// Returns false if the transport should use raw server position (no interpolation).
+    [[nodiscard]] bool computePathTime(
+        ActiveTransport& transport,
+        const math::CatmullRomSpline& spline,
+        double elapsedTime,
+        float deltaTime,
+        uint32_t& outPathTimeMs) const;
+
+    /// Process a server position update: update clock offset, detect yaw flips,
+    /// bootstrap velocity, and switch between client/server driven modes.
+    void processServerUpdate(
+        ActiveTransport& transport,
+        const PathEntry* pathEntry,
+        const glm::vec3& position,
+        float orientation,
+        double elapsedTime);
+
+private:
+    /// Detect and apply 180-degree yaw correction based on movement vs heading alignment.
+    void updateYawAlignment(
+        ActiveTransport& transport,
+        const glm::vec3& velocity) const;
+
+    /// Bootstrap velocity from nearest DBC path segment on first authoritative sample.
+    void bootstrapVelocityFromPath(
+        ActiveTransport& transport,
+        const PathEntry& pathEntry) const;
+};
+
+} // namespace wowee::game