READONLY mode support is needed in dotnet MCP server as implemented in Node version

Could you please implement support for `READONLY` mode in dotnet version?
So that when `env` configuration is configured with `"READONLY": "true"` MCP server will not allow to execute Update/Insert/Drop tools.

```
"env": {
"CONNECTION_STRING": "Server=localdev;Database=eCommerce;Integrated Security=True;TrustServerCertificate=True;Encrypt=False",
"READONLY": "true"
}
```

dotnet version:
https://github.com/Azure-Samples/SQL-AI-samples/blob/5a4ba3f8d62aa5683a497f16e5ff4c26cc600ee0/MssqlMcp/dotnet/MssqlMcp/Program.cs#L37

Node version:
https://github.com/Azure-Samples/SQL-AI-samples/blob/5a4ba3f8d62aa5683a497f16e5ff4c26cc600ee0/MssqlMcp/Node/src/index.ts#L85

Start in MssqlMcp/dotnet/MssqlMcp/Program.cs at line 37 and compare the existing READONLY handling in MssqlMcp/Node/src/index.ts at line 85. Trace how the Update, Insert, and Drop tools are registered or executed, then verify that setting READONLY to true prevents all three while other tools remain available.

Scritto dal modello di indicizzazione a partire dal testo della issue.