docs: clarify Docker installation requirements and add platform-specific instructions

- Replace "Docker Desktop" prerequisite with generic "Docker installed"
- Add detailed Docker installation instructions for macOS, Linux, and Windows
- Include package manager options (Homebrew, apt-get, winget, Chocolatey)
- Add Docker verification command
- Update related documentation files for consistency
- Use collapsible section to keep Quick Start clean

Now users understand they can use any Docker installation method, not just Docker Desktop.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

docs/DOCKER_README.md

@@ -5,7 +5,7 @@ This guide provides comprehensive instructions for deploying n8n-MCP using Docke
 ## 🚀 Quick Start
 
 ### Prerequisites
-- Docker Engine 20.10+ or Docker Desktop
+- Docker Engine 20.10+ (Docker Desktop on Windows/macOS, or Docker Engine on Linux)
 - Docker Compose V2
 - (Optional) openssl for generating auth tokens