Migrate the ClickUp issue provider from a tightly-coupled Angular
service to the external plugin architecture, following the pattern
established by the GitHub provider migration.
- Delete all built-in ClickUp files (api service, models, components,
tests, constants) from src/app/features/issue/providers/clickup/
- Create new plugin in packages/plugin-dev/clickup-issue-provider/
with pure-function API layer, plugin registration, i18n, and tests
- Add migration in issue-provider.reducer.ts to convert old ClickUp
provider config to plugin shape (preserves legacy fields for rollback)
- Move CLICKUP from BuiltInIssueProviderKey to MigratedIssueProviderKey
- Register clickup-issue-provider as bundled plugin
- Fix isDone detection: use status.type instead of status.status so
custom closed statuses like "Shipped" are correctly detected
- Show disabled plugin issue providers in setup overview for
discoverability — clicking auto-enables and opens config dialog
