[Remove Vuetify from Studio] Replace the remaining VAutocomplete dropdowns with KMultiSelect

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Overview

Studio still uses the Vuetify component VAutocomplete in three shared form components. The Kolibri Design System now has KMultiSelect, which does the same job. Two components already made this change, so the pattern is set.

Scope

Included

• contentcuration/contentcuration/frontend/shared/views/LanguageDropdown.vue
• contentcuration/contentcuration/frontend/shared/views/contentNodeFields/CompletionOptions/ActivityDuration.vue
• contentcuration/contentcuration/frontend/shared/views/form/CountryField.vue
• contentcuration/contentcuration/frontend/shared/views/contentNodeFields/CategoryOptions.vue
• The files that use these components, where they pass Vuetify props to the dropdown.
• The tests for these components.

Excluded:

• The other Vuetify components in the same files.
• DropdownWrapper, because other components still use it.
• The removal of VAutocomplete from shared/app.js. That happens after every use of it is gone.

Guidance

• Set up Studio with the steps in README.md.
• Read the KMultiSelect documentation: https://design-system.learningequality.org/kmultiselect
• Follow the two finished examples: LanguageFilter.vue (#6093) and CategoryOptions.vue (#6092).
• Shared accessibility strings live in shared/strings/commonStrings.js. Add a new string only when no shared string exists.
• KMultiSelect uses the props invalid and invalidText. It does not use the Vuetify rules prop.

Strategy

Testing Requirements

• Write new tests with Vue Testing Library. Do not add tests with @vue/test-utils.
• pnpm test and pre-commit run --all-files must pass on each task.

AI usage

I used Claude Code to draft this issue. I set the scope, checked the file list, and wrote the guidance.

Start with the four listed Vue components and compare them with the completed LanguageFilter.vue and CategoryOptions.vue examples, then read the KMultiSelect documentation. Update the remaining dropdown usages and their component tests, ensuring the listed test commands pass and no VAutocomplete usage remains in the scoped files.