refactor: extract spline math, consolidate packet parsing, decompose TransportManager

Extract CatmullRomSpline (include/math/spline.hpp, src/math/spline.cpp) as a
standalone, immutable, thread-safe spline module with O(log n) binary segment
search and fused position+tangent evaluation — replacing the duplicated O(n)
evalTimedCatmullRom/orientationFromTangent pair in TransportManager.

Consolidate 7 copies of spline packet parsing into shared functions in
game/spline_packet.{hpp,cpp}: parseMonsterMoveSplineBody (WotLK/TBC),
parseMonsterMoveSplineBodyVanilla, parseClassicMoveUpdateSpline,
parseWotlkMoveUpdateSpline, and decodePackedDelta. Named SplineFlag constants
replace magic hex literals throughout.

Extract TransportPathRepository (game/transport_path_repository.{hpp,cpp}) from
TransportManager — owns path data, DBC loading, and path inference. Paths stored
as PathEntry wrapping CatmullRomSpline + metadata (zOnly, fromDBC, worldCoords).
TransportManager reduced from ~1200 to ~500 lines, focused on transport lifecycle
and server sync.

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

include/math/spline.hpp

@@ -0,0 +1,77 @@
+// include/math/spline.hpp
+// Standalone Catmull-Rom spline module with zero external dependencies beyond GLM.
+// Immutable after construction — thread-safe for concurrent reads.
+#pragma once
+#include <glm/glm.hpp>
+#include <glm/gtc/quaternion.hpp>
+#include <vector>
+#include <cstdint>
+
+namespace wowee::math {
+
+/// A single time-indexed control point on a spline.
+struct SplineKey {
+    uint32_t timeMs;
+    glm::vec3 position;
+};
+
+/// Result of evaluating a spline at a given time — position + tangent.
+struct SplineEvalResult {
+    glm::vec3 position;
+    glm::vec3 tangent;       // Unnormalized derivative
+};
+
+/// Immutable spline path. Constructed once, evaluated many times.
+/// Thread-safe for concurrent reads after construction.
+class CatmullRomSpline {
+public:
+    /// Construct from time-sorted keys.
+    /// If `timeClosed` is true, the path wraps: first and last keys share endpoints.
+    /// If false, uses clamped endpoints (no wrapping).
+    explicit CatmullRomSpline(std::vector<SplineKey> keys, bool timeClosed = false);
+
+    /// Evaluate position at given path time (clamped to [0, duration]).
+    [[nodiscard]] glm::vec3 evaluatePosition(uint32_t pathTimeMs) const;
+
+    /// Evaluate position and tangent at given path time.
+    [[nodiscard]] SplineEvalResult evaluate(uint32_t pathTimeMs) const;
+
+    /// Derive orientation quaternion from tangent (Z-up convention).
+    [[nodiscard]] static glm::quat orientationFromTangent(const glm::vec3& tangent);
+
+    /// Total duration of the spline in milliseconds.
+    [[nodiscard]] uint32_t durationMs() const { return durationMs_; }
+
+    /// Number of control points.
+    [[nodiscard]] size_t keyCount() const { return keys_.size(); }
+
+    /// Direct access to keys (for path inference, etc.).
+    [[nodiscard]] const std::vector<SplineKey>& keys() const { return keys_; }
+
+    /// Whether this spline has meaningful XY movement (not just Z-only like elevators).
+    [[nodiscard]] bool hasXYMovement(float minRange = 1.0f) const;
+
+    /// Find nearest key index to a world position (for phase estimation).
+    [[nodiscard]] size_t findNearestKey(const glm::vec3& position) const;
+
+    /// Whether the spline is time-closed (wrapping).
+    [[nodiscard]] bool isTimeClosed() const { return timeClosed_; }
+
+private:
+    /// Binary search for segment containing pathTimeMs. O(log n).
+    [[nodiscard]] size_t findSegment(uint32_t pathTimeMs) const;
+
+    /// Get 4 control points {p0,p1,p2,p3} for the segment starting at `segIdx`.
+    struct ControlPoints { glm::vec3 p0, p1, p2, p3; };
+    [[nodiscard]] ControlPoints getControlPoints(size_t segIdx) const;
+
+    /// Evaluate position and tangent for a segment at parameter t in [0,1].
+    [[nodiscard]] SplineEvalResult evalSegment(
+        const ControlPoints& cp, float t) const;
+
+    std::vector<SplineKey> keys_;
+    bool timeClosed_;
+    uint32_t durationMs_;
+};
+
+} // namespace wowee::math