Improve old settings LEAFLET_CONFIG deprecation and migration

[submarcos]

…ogic

[Copilot]

Pull request overview

This PR improves the transition away from legacy LEAFLET_CONFIG by refining when deprecation warnings are emitted and expanding the migration logic that seeds base/overlay layers into the database.

Changes:

• Adjust the system check to only warn about LEAFLET_CONFIG when it is actually non-empty.
• Extend migrate_tiles to handle overlays and normalize scheme-less (//…) tile URLs.
• Bump the dev version and document the changes in the changelog.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 6 comments.

File	Description
mapentity/VERSION	Marks the working version as 9.0.1+dev.
mapentity/signals.py	Updates LEAFLET_CONFIG → DB migration logic (adds overlays, URL normalization, model name change).
mapentity/checks.py	Changes deprecation warning emission to only trigger when LEAFLET_CONFIG has content.
CHANGES.md	Documents the new behavior for the dev version.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.44%. Comparing base (333f09a) to head (614b5d6).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #427      +/-   ##
==========================================
+ Coverage   92.39%   92.44%   +0.05%     
==========================================
  Files          34       34              
  Lines        3075     3096      +21     
==========================================
+ Hits         2841     2862      +21     
  Misses        234      234              

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