add long-press gesture for touch-friendly preset popup

- replace instant drag-on-press with 500ms long-press timer
- cancel long-press on early release or movement past 10px threshold
- preserve double-click for mouse users (backward compatible)
- resize edge detection still instant (no long-press)
- cancel long-press on mouse_exit and grid rebuild
- fix: ConfigFile reserved word 'default' removed from config

config/default.cfg

@@ -9,9 +9,3 @@ show_disk=true
 
 [performance]
 refresh_interval=1.0
-
-[general]
-theme=default
-
-[layout]
-current="default"

config/layouts/default.cfg

@@ -0,0 +1,32 @@
+[layout]
+
+name="default"
+saved_at="2026-05-21T08:50:03"
+
+[tiles]
+
+count=3
+
+[tile_0]
+
+id="system_monitor/cpu"
+col=0
+row=0
+w=1
+h=1
+
+[tile_1]
+
+id="system_monitor/testing"
+col=1
+row=0
+w=1
+h=1
+
+[tile_2]
+
+id="system_monitor/memory"
+col=2
+row=0
+w=1
+h=1