Add Unified Diff MCP Server - HTML/PNG diff visualization tool

## Summary
Adding Unified Diff MCP Server to the Community Servers section.

## Description  
- **Beautiful HTML and PNG diff visualization** using diff2html
- **High-performance processing** with Bun runtime
- **Seamless integration** with filesystem edit_file dry-run output
- **Cross-platform support** (Windows/macOS/Linux)
- **Fixed filename output** for disk space efficiency

## Repository
https://github.com/gorosun/unified-diff-mcp

Following the contribution guidelines: alphabetical order maintained in Community Servers section.

README.md

@@ -393,6 +393,7 @@ Tools and integrations that enhance the development workflow and environment man
 - [flipt-io/mcp-server-flipt](https://github.com/flipt-io/mcp-server-flipt) 📇 🏠 - Enable AI assistants to interact with your feature flags in [Flipt](https://flipt.io).
 - [GLips/Figma-Context-MCP](https://github.com/GLips/Figma-Context-MCP) 📇 🏠 - Provide coding agents direct access to Figma data to help them one-shot design implementation.
 - [gofireflyio/firefly-mcp](https://github.com/gofireflyio/firefly-mcp) 🎖️ 📇 ☁️ - Integrates, discovers, manages, and codifies cloud resources with [Firefly](https://firefly.ai).
+- [gorosun/unified-diff-mcp](https://github.com/gorosun/unified-diff-mcp) 📇 🏠 - Generate and visualize unified diff comparisons with beautiful HTML/PNG output, supporting side-by-side and line-by-line views for filesystem dry-run integration
 - [Govcraft/rust-docs-mcp-server](https://github.com/Govcraft/rust-docs-mcp-server) 🦀 🏠 - Provides up-to-date documentation context for a specific Rust crate to LLMs via an MCP tool, using semantic search (embeddings) and LLM summarization.
 - [haris-musa/excel-mcp-server](https://github.com/haris-musa/excel-mcp-server) 🐍 🏠 - An Excel manipulation server providing workbook creation, data operations, formatting, and advanced features (charts, pivot tables, formulae).
 - [higress-group/higress-ops-mcp-server](https://github.com/higress-group/higress-ops-mcp-server) 🐍 🏠 - MCP server that provides comprehensive tools for managing [Higress](https://github.com/alibaba/higress) gateway configurations and operations.