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/core/application.hpp

@@ -113,7 +113,7 @@ public:
     // World loader access
     WorldLoader* getWorldLoader() { return worldLoader_.get(); }
 
-    // Audio coordinator access (Section 4.1: extracted audio subsystem)
+    // Audio coordinator access
     audio::AudioCoordinator* getAudioCoordinator() { return audioCoordinator_.get(); }
 
 private: