feat(Lifecycle)!: use craft-application's new plugin groups

[lengau]

Breaking change: We're extending the MINIMAL plugin group rather than the DEFAULT plugin group so that we can pick upstream plugins as needed, ensuring they work with imagecraft.

Fixes #314
IMAGECRAFT-121

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[Copilot]

Pull request overview

Updates Imagecraft’s lifecycle/plugin integration to use craft-application’s new “plugin groups” mechanism, switching the baseline group to MINIMAL so upstream plugins can be selected more explicitly for Imagecraft compatibility.

Changes:

• Add ImagecraftLifecycleService.get_plugin_group() to return PluginGroup.MINIMAL plus Imagecraft-specific plugins.
• Remove Imagecraft._get_app_plugins() override from the main Application class (plugin selection now handled via lifecycle plugin groups).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
imagecraft/services/lifecycle.py	Introduces get_plugin_group() to merge MINIMAL group plugins with Imagecraft’s custom plugins.
imagecraft/application.py	Removes the legacy app plugin hook that’s superseded by the new plugin-group mechanism.

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