feat: Developer Experience Overhaul — README restructure + multi-platform setup

[jdrhyne]

Summary

This PR overhauls the README for significantly improved developer experience, establishing consistency with the DWS MCP server and making it easier for developers to discover, understand, and adopt the Nutrient Document Engine MCP Server.

Changes

README.md

• Value-first positioning: Lead with capabilities, not infrastructure
• Multi-platform Quick Start: Collapsible setup instructions for Claude Desktop, Cursor, Windsurf, VS Code (Copilot), and generic MCP clients (stdio + HTTP)
• Comprehensive Available Tools tables: All 21 tools organized by category (Discovery, Extraction, Editing, Annotations, Forms, Security, System)
• Why Nutrient? section: Competitive positioning with the 'Read-Write Gap' narrative, emphasizing self-hosted privacy story
• Troubleshooting section: Docker, connectivity, dashboard, and client issues
• AI framework compatibility list: Claude, Cursor, Windsurf, VS Code, LangChain, OpenAI Agents
• Improved Examples & Documentation: Table format with descriptions
• Consistent structure: Mirrors DWS MCP server README structure for brand consistency

package.json

• Added keywords for better npm discoverability: pdf, document-processing, ai, agent, mcp-server, redaction, forms, annotations, model-context-protocol

Testing

• All 179 unit tests pass ✅
• Integration tests correctly skip without Document Engine (expected)
• ESLint clean ✅
• No code changes — README and package.json metadata only

Context

Part of a coordinated DX overhaul across both Nutrient MCP servers to establish consistent, best-in-class developer experience. See companion PR on nutrient-dws-mcp-server: PSPDFKit/nutrient-dws-mcp-server#11