feat: expand Files features; add file associations

programs/src/desktop/apps/filemanager/app.cpp

@@ -37,6 +37,7 @@ static void open_filemanager_internal(DesktopState* ds, const char* initial_path
     FileManagerState* fm = (FileManagerState*)montauk::malloc(sizeof(FileManagerState));
     montauk::memset(fm, 0, sizeof(FileManagerState));
     fm->selected = -1;
+    fm->sel_anchor = -1;
     fm->last_click_item = -1;
     fm->history_pos = -1;
     fm->history_count = 0;