Introduce EditorSettings as the effective, source-agnostic editor configuration
the editor and save path obey. .editorconfig is demoted to one *source*
(editorconfig.dart now returns EditorSettings); editor_settings_resolver.dart is
the single composition seam where future sources — a settings panel, a clide
settings file — layer in via merge() without the editor changing.
The registry resolves settings on buffer load and, when a .editorconfig is saved
in-app, re-resolves every open buffer and emits editor.settings-changed (a hook
in save, not a filesystem watcher — the realistic case, cheaply). Buffer JSON
carries editorSettings. 100% line coverage on the new model + resolver.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
jpmschweitzerandClaude Opus 4.8
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