refs https://github.com/TryGhost/Admin/pull/2209
- `miragejs` has been extracted to a framework-independent library, the re-exports of `miragejs` elements in `ember-cli-mirage` have been deprecated making our test logs very noisy
- added `miragejs` as a top-level dependency
- updated all relevant imports to pull from `miragejs` instead of `ember-cli-mirage`
no issue
- moved navigation settings tests from old settings/design tests to a separate file and unskipped them
- added happy-path acceptance tests for
- rendering design screen
- installing an official theme from the themes list
- uploading a custom theme
closes https://github.com/TryGhost/Ghost/issues/8127
- update theme activation to manually set other themes to `active: false` in the store now that we only the active theme back from `/themes/:name/activate` endpoint
- move theme warning list item rendering into `{{gh-theme-error-li error=x}}`
- add `theme-warnings` modal that accepts a warnings list, title, and optional message
- after activating a theme, check if the theme has any warnings or errors and display an appropriate modal informing the user
requires https://github.com/TryGhost/Ghost/pull/8093
- adds `theme.activate()` method and associated adapter method for activating themes rather than relying on `settings.activeTheme`
- minor refactors to the `modals/upload-theme` component to use a full theme model
