fix progress state on Vue nodes in subgraphs (#5842)

## Summary

Fixes two errors with subgraph progress states:

1. Nodes inside subgraphs were not having progress state shown
2. Subgraph nodes (outer representation) themselves did not have a
visible progress state

1 is fixed by using locator IDs instead of local node IDs.

2 is fixed by ensuring the subgraph title button does not wrap to a
newline and thus block the progress bar under the node header.

## Changes

- **What**: Updated `useNodeExecutionState` composable to use
`nodeLocatorId` for tracking execution state across subgraph boundaries
- **What**: Modified NodeHeader layout to fix subgraph enter button
positioning with proper flexbox gap

## Review Focus

Execution state tracking accuracy for nested subgraph nodes and
NodeHeader layout consistency across different node types.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5842-fix-progress-state-on-Vue-nodes-in-subgraphs-27c6d73d365081cb8335c8bb5dbd74f7)
by [Unito](https://www.unito.io)

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Co-authored-by: github-actions <[email protected]>

Author: christian-byrne