fix: bugs surfaced by new gtest coverage

- html.cpp: rgba() colors parsed with setRedF/GreenF/BlueF (0-1) while the
  writer emits 0-255 integers, so semi-transparent text colors lost their
  RGB on round-trip; parse with integer setters instead
- CLIProgressDialog: percentage padding compared normalized progress
  (0.0-1.0) against 10/100, so padding was always fully applied; compute
  the percentage first
- TimelineUndoPointer BlockTrimCommand: remove_block_from_graph_ was
  never initialized (UB on redo)
- TimelineUndoGeneral TransitionRemoveCommand: track_ was never
  initialized; GetRelevantProject() could dereference it before redo()
- ProjectLoadTask::Run(): failure path deleted project_ without
  resetting it, leaving GetLoadedProject() dangling

app/task/project/load/load.cpp

@@ -82,6 +82,7 @@ bool ProjectLoadTask::Run()
 		return true;
 	} else {
 		delete project_;
+		project_ = nullptr;
 		return false;
 	}
 }