fix: drag-to-transfer drop not triggering transfer dialog

s_dropTargetIdx was reset to -1 unconditionally each frame, including
the release frame. Since drop target detection runs in PASS 2 (after
the drop handler), the target was always -1 when checked. Only reset
while mouse button is held so the previous frame's value is preserved.

Also bump version to 1.2.0-rc1 and add release notes.

CMakeLists.txt

@@ -20,6 +20,9 @@ project(ObsidianDragon
     DESCRIPTION "DragonX Cryptocurrency Wallet"
 )
 
+# Pre-release suffix (e.g. "-rc1", "-beta2"). Leave empty for stable releases.
+set(DRAGONX_VERSION_SUFFIX "-rc1")
+
 # C++17 standard
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)