Fix the custom background translation strings

data/core.yaml

@@ -434,8 +434,6 @@ en:
     best_imagery: Best known imagery source for this location
     switch: Switch back to this background
     custom: Custom
-    custom_button: Edit custom background
-    custom_prompt: "Enter a tile URL template. Valid tokens are:\n   - {zoom} or {z}, {x}, {y} for Z/X/Y tile scheme\n   - {-y} or {ty} for flipped TMS-style Y coordinates\n   - {u} for quadtile scheme\n   - {switch:a,b,c} for DNS server multiplexing\n\nExample:\n{example}"
     overlays: Overlays
     imagery_source_faq: Imagery Info / Report a Problem
     reset: reset
@@ -514,6 +512,11 @@ en:
     full:
       description: Full Fill
       tooltip: "Areas are drawn fully filled."
+  settings:
+    custom_background:
+      tooltip: Edit custom background
+      heading: Custom Background Settings
+      instructions: "Enter a tile URL template. Valid tokens are:\n   - {zoom} or {z}, {x}, {y} for Z/X/Y tile scheme\n   - {-y} or {ty} for flipped TMS-style Y coordinates\n   - {u} for quadtile scheme\n   - {switch:a,b,c} for DNS server multiplexing\n\nExample:\n{example}"
   restore:
     heading: You have unsaved changes
     description: "Do you wish to restore unsaved changes from a previous editing session?"