Added the feature for custom backgrounds

[JaiswalShivang]

feat: Multiple custom background layers with CRUD operations

Fixes #8874

Summary

This PR enables users to add, edit, name, and delete multiple custom background layers in the iD editor. Previously, only a single custom background was supported.

Demo Video

2026-02-05.22-21-29.mp4

Note: The video demonstrates adding, editing, naming, and deleting multiple custom backgrounds.

Changes

User-Facing Changes

• Multiple Custom Backgrounds: Users can now add unlimited custom background layers
• Dedicated Section: New "Custom Backgrounds" section in the Background pane
• Named Backgrounds: Each custom background can have an optional name
• URL Fallback: Backgrounds without names display a truncated URL (e.g., "Custom: tiles.example.com/berlin/…")
• Add/Edit/Delete: Full CRUD operations with intuitive icons (pencil for edit, trash for delete)
• Delete with Confirmation: Confirmation dialog to prevent accidental data loss
• "Custom:" Prefix: All custom backgrounds are clearly labeled with "Custom:" prefix
• Data Persistence: All custom backgrounds persist across sessions

Technical Changes

1. Data Format: Custom backgrounds stored as JSON array in background-custom-templates preference:

   [
     { "id": "custom-1", "name": "My Tiles", "template": "https://..." },
     { "id": "custom-2", "name": "Berlin 2025", "template": "https://..." }
   ]

[Copilot]

Pull request overview

This PR implements support for multiple custom background layers in the iD editor, addressing issue #8874. Previously, only a single custom background was supported. The implementation adds full CRUD operations for managing multiple named custom backgrounds with data persistence across sessions.

Changes:

• Adds support for multiple custom backgrounds stored as JSON array in background-custom-templates preference
• Implements UI for adding, editing, naming, and deleting custom backgrounds directly in the background list
• Includes migration logic to convert existing single custom background to new multi-background format

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 19 comments.

Show a summary per file

File	Description
modules/ui/settings/custom_background.js	Modified to support editing both new and existing custom backgrounds with name and template fields
modules/ui/sections/custom_background_list.js	New file (unused) that appears to be a duplicate/abandoned implementation
modules/ui/sections/background_list.js	Integrated custom backgrounds list with edit/delete buttons into main background pane
modules/renderer/background_source.js	Updated Custom factory to accept id and name parameters, show "Custom: {name}" prefix
modules/renderer/background.js	Added migration logic and multi-custom background initialization
data/core.yaml	Added localization strings for custom backgrounds UI
css/80_app.css	Added styling for custom background list items and action buttons

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[JaiswalShivang]

@tordans - Thank you again for your detailed feedback on PR #11836. I've completely rewritten the implementation based on your guidance.
All Copilot AI feedback has been addressed:

• No page reloads (dynamic UI updates)
• Proper icons and i18n
• Delete confirmation dialog
• Input validation
• Clean code with no dead files
  The PR is ready for your review. I appreciate your patience and mentorship!