Multi-select widget missing remote support

## Recommendation

### 🔧 FINISH: Add remote data support to multi-select widget

Single-select combo widgets have remote data support; multi-select does not.

## What Was Found

- `src/renderer/extensions/vueNodes/widgets/composables/useComboWidget.ts:74` — `// TODO: Add remote support to multi-select widget` with explicit issue link (#3003).

## Context

Remote support allows dropdowns to fetch options from API sources. This is implemented for single-select but not multi-select.

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**Category:** Half-Implemented | **Confidence:** HIGH | **Tools:** Semantic analysis
_Filed by audit-code skill_

Part of #11022

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-11047-Multi-select-widget-missing-remote-support-33e6d73d3650811da98be8f34e5bdee9) by [Unito](https://www.unito.io)