Improve Git History navigation and asynchronous UI safety

Add a History ref selector for HEAD, local branches, remote branches, and tags without requiring checkout. Reuse cached branch-model display strings to keep large ref lists efficient.
Make deferred main-thread callbacks lifetime-safe across ecode controllers and plugins. Initialize plugin dispatchers during UIReady and extend MainThreadLifetime to support delayed and tagged dispatch.
Fix expandable Git History rows, empty merge projections, and commit-description expansion. Display only the physical first line while collapsed and avoid duplicating it in the expanded body.
Add coverage for history ref handling and preserve stale-request guards during repository and revision changes.
Fix UIImageViewer dimension reporting for sprites by displaying the underlying texture dimensions.
The Git History interface remains a work in progress.

include/eepp/scene/event.hpp

@@ -134,6 +134,7 @@ class EE_API Event {
 		OnApply,
 		OnShowFindReplace,
 		OnHideFindReplace,
+		OnTooltipCreated,
 		NoEvent = eeINDEX_NOT_FOUND
 	};
 

include/eepp/scene/mainthreadlifetime.hpp

@@ -30,7 +30,8 @@ template <typename T> class MainThreadLifetime {
 	  public:
 		WeakHandle() = default;
 
-		void run( std::function<void( T* )> callback ) const {
+		void run( std::function<void( T* )> callback, const Time& delay = Time::Zero,
+				  Action::UniqueID tag = 0 ) const {
 			auto state = mState.lock();
 			if ( !state )
 				return;
@@ -49,7 +50,8 @@ template <typename T> class MainThreadLifetime {
 					}
 					if ( object )
 						callback( object );
-				} );
+				},
+				delay, tag );
 		}
 
 		explicit operator bool() const { return !mState.expired(); }