fix: EndOfBookOptions fails to compile

ActivityManager.h forward-declares Activity but holds
std::unique_ptr<Activity> members. Instantiating that unique_ptr's
destructor requires the complete type, so any TU including
ActivityManager.h without Activity.h fails to compile.

Include Activity.h directly. Adding it to ActivityManager.h instead does
not work: Activity.h depends on HomeMenuItem, which ActivityManager.h
defines.

src/activities/reader/EndOfBookOptions.cpp

@@ -6,6 +6,10 @@
 
 #include "CrossPointSettings.h"
 #include "ReaderUtils.h"
+// ReaderUtils.h pulls in ActivityManager.h, which only forward-declares Activity while holding
+// std::unique_ptr<Activity> members. Destroying that unique_ptr needs the complete type, so the
+// definition must be visible here.
+#include "activities/Activity.h"
 #include "components/UITheme.h"
 #include "fontIds.h"
 #include "util/ButtonNavigator.h"