Dockerfile improved build process

[kesku]

Summary

Fixed and documente Docker setup for the MCP Server. Dockerfile now properly builds TypeScript code and creates an optimized production image.

Changes

• Fix Dockerfile to properly build TypeScript (npm run build) before creating release image
• Add --ignore-scripts flag to npm install to prevent prepare script from running before source files are copied
• Add DOCKER.md with build instructions, usage

Misc

Users can now build and run the server with Docker properly:

# Build the image
docker build -t perplexity-mcp-server .

# Run with API key
docker run --rm -e PERPLEXITY_API_KEY=your_key_here perplexity-mcp-server

# Or with custom timeout and proxy
docker run --rm \
  -e PERPLEXITY_API_KEY=your_key_here \
  -e PERPLEXITY_TIMEOUT_MS=600000 \
  -e PERPLEXITY_PROXY=https://your-proxy-host:8080 \
  perplexity-mcp-server