docs: Update nuget/README.md with MCP endpoint and comprehensive content

[Copilot]

Why make this change?

nuget/README.md (the README shown on the NuGet package page) was minimal and stale — it described only REST and GraphQL, omitted the MCP endpoint entirely, and lacked database/environment support tables, getting started steps, and other content present in the root README.md.

What is this change?

Rewrote nuget/README.md to match the quality and completeness of the root README.md, adapted for the NuGet context:

• Badges — NuGet version, download count, docs link, license
• About — updated to cover REST, GraphQL, and MCP endpoints
• Support tables — databases (Azure SQL, SQL Server, SQLDW, Cosmos DB, PostgreSQL, MySQL), environments (On-Prem/Azure/AWS/GCP/Other), and endpoints (REST ✅ GraphQL ✅ MCP ✅)
• Features — added MCP section: DML tools, custom tools via stored procedures, configurable path (/mcp default), AI client compatibility (GitHub Copilot, Azure AI Foundry)
• Getting started — install → init config → add entity → dab start → access /api, /graphql, /mcp
• Resources/Contributing/Trademarks — aligned with root README; links use absolute GitHub URLs (required in NuGet context)

How was this tested?

• Integration Tests
• Unit Tests

Documentation-only change; no code logic modified.

Sample Request(s)

After dab start, all three endpoints are available:

GET  http://localhost:5000/api/Todo       # REST
     http://localhost:5000/graphql        # GraphQL (Nitro UI)
     http://localhost:5000/mcp            # MCP
     http://localhost:5000/api/openapi    # Swagger UI
     http://localhost:5000/health         # Health