Add custom KiCad autocomplete list settings

[DanTrackpaw]

Summary

Add admin settings for KiCad autocomplete lists.

This change keeps the autogenerated default KiCad lists read-only and introduces editable custom override files:

• public/kicad/footprints_custom.txt
• public/kicad/symbols_custom.txt

A new setting controls whether KiCad autocomplete uses the autogenerated defaults or the custom files.

What changed

• Added a useCustomList KiCad setting
• Updated KiCad autocomplete fields to use either the default or custom list files
• Updated the admin editor page to:
  • show custom files as editable
  • show default files as read-only reference
• Added seeded custom files with a comment header
• Updated docs and translations
• Extended the controller test coverage

Behavior

• Default KiCad lists remain autogenerated and unchanged
• Custom lists are stored separately and can be edited in the UI
• When Use custom autocomplete lists is enabled, autocomplete uses the custom files instead of the default files
• This is a full switch, not a merge of default and custom entries

Why this approach

This avoids editing autogenerated files directly and keeps user-maintained autocomplete entries stable across updates, while keeping the implementation small
and localized.

Verification

• Verified locally in Docker
• Ran the focused PHPUnit test:
  • tests/Controller/KicadListEditorControllerTest.php