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/ui/chat_panel.hpp

@@ -110,14 +110,14 @@ public:
     /** Reset all chat settings to defaults. */
     void restoreDefaults();
 
-    // Section 3.5: UIServices injection (Phase B singleton breaking)
+    // UIServices injection (Phase B singleton breaking)
     void setServices(const UIServices& services) { services_ = services; }
 
     /** Replace $g/$G and $n/$N gender/name placeholders in quest/chat text. */
     std::string replaceGenderPlaceholders(const std::string& text, game::GameHandler& gameHandler);
 
 private:
-    // Section 3.5: Injected UI services (Phase B singleton breaking)
+    // Injected UI services (Phase B singleton breaking)
     UIServices services_;
 
     // ---- Chat input state ----