Refine README description to focus on user-facing functionality

[Copilot]

The README description referenced internal implementation details ("Asset Optimization workflow", "ISyncRef") rather than describing what users can do with the mod.

Changes:

• Rewrote short description to emphasize user-facing functionality: a find-and-replace dialog for references within slot hierarchies
• Highlighted key features: analysis preview and undo batch support
• Removed technical jargon requiring knowledge of Resonite internals

Before:

A mod that mirrors the Asset Optimization workflow to bulk swap every matching `ISyncRef` inside a single undo batch.

After:

A mod that provides a userspace dialog for bulk replacement of references. Find and replace all references pointing to one element with references to another element within a slot hierarchy, with analysis preview and undo support.

Original prompt

Refine short description of README.md based on the key feature implemented.

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