fix(onboarding): fix widget links, isComplete logic, and event slugs

Use dynamic href for external links, check completedAt for graduation,
link events by slug instead of _id, and remove stale click handler.

tests/client/composables/useOnboarding.test.js

@@ -233,7 +233,7 @@ describe('useOnboarding', () => {
     })
 
     expect(currentSuggestion.value.key).toBe('wiki')
-    expect(currentSuggestion.value.action).toBeNull()
+    expect(currentSuggestion.value.action).toBe('https://wiki.ghostguild.org')
     expect(currentSuggestion.value.isExternal).toBe(true)
   })