Video paste does not create a node

## Recommendation

### 🔧 FINISH: Implement video node creation on paste

When pasting video content with no video node selected, nothing happens. Audio and image paste both work correctly.

## What Was Found

- `src/composables/usePaste.ts:119-126` — The video paste branch contains only `// TODO: when video node exists` with no implementation.

## Evidence

Audio paste creates an audio node, image paste creates an image node, but video paste is a no-op in this code path.

## Context

The paste composable handles image, audio, and video content types. Video was stubbed but never completed.

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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-11037-Video-paste-does-not-create-a-node-33e6d73d3650812e9654d362d2b5e797) by [Unito](https://www.unito.io)