refactor(activation): clean up ActivationModal component and remove unused pages

- Removed the `onComplete` prop from the `ActivationModal` component to streamline its functionality.
- Deleted several unused pages including `apikeys.vue`, `changelog.vue`, `flashbackup.vue`, `index.vue`, `login.query.ts`, `login.vue`, `redirect.vue`, `welcome.vue`, `apikeyauthorize.vue`, and `test-update-modal.vue` to improve codebase maintainability.
- This update enhances the clarity and performance of the application by eliminating unnecessary files and simplifying the component structure.

web/src/components/Activation/ActivationModal.vue

@@ -222,7 +222,6 @@ const currentStepProps = computed<Record<string, unknown>>(() => {
         ...baseProps,
         currentVersion: currentVersion.value,
         previousVersion: previousVersion.value,
-        onComplete: closeModal,
         onSkip: undefined,
         showSkip: false,
       };