Port route 4-c: NPC shop (PythonShop.cpp) + app cursor state

- UserInterface/PythonShop.cpp ported verbatim (shop module, initshop after initfly);
  pending stub and module stubs removed.
- 40250 PythonApplicationCursor.cpp and SetMouseHandler moved into the platform
  CPythonApplication on file-static members; GetCursorNum out of line, since uishop's
  app.GetCursor() dereferenced the missing application object.
- Fake server: general store (npclist 9003) answers CG_ON_CLICK with GC_SHOP START,
  CG_SHOP BUY/SELL2/END like CShop::Buy / CShopManager::Sell.
- port.login_flow step 10: click the shopkeeper, right-click buy, drag-sell, ESC close.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

extension/src/platform/pending/UserInterface/PythonShop.cpp

@@ -1,48 +0,0 @@
-// Stand-in for the 40250 logic unit UserInterface/PythonShop.cpp, not ported yet: the members the ported units
-// reference, as platform_stub.py stubs. Delete this file in the commit that ports the unit into port/
-// (docs/PORT-PLAN.md).
-#include "UserInterface/StdAfx.h"
-#include "UserInterface/PythonShop.h"
-
-#include "../../PlatformStub.h"
-
-CPythonShop::CPythonShop()
-{
-	MT_PLATFORM_STUB();
-}
-
-CPythonShop::~CPythonShop()
-{
-	MT_PLATFORM_STUB();
-}
-
-auto CPythonShop::Clear() -> void
-{
-	MT_PLATFORM_STUB();
-}
-
-auto CPythonShop::SetItemData(DWORD, const TShopItemData &) -> void
-{
-	MT_PLATFORM_STUB();
-}
-
-auto CPythonShop::SetItemData(BYTE, DWORD, const TShopItemData &) -> void
-{
-	MT_PLATFORM_STUB();
-}
-
-auto CPythonShop::SetTabCoinType(BYTE, BYTE) -> void
-{
-	MT_PLATFORM_STUB();
-}
-
-auto CPythonShop::SetTabName(BYTE, const char *) -> void
-{
-	MT_PLATFORM_STUB();
-}
-
-auto CPythonShop::IsOpen() -> BOOL
-{
-	MT_PLATFORM_STUB();
-	return mt_platform_stub_return<BOOL>();
-}