Add configurable OAuth token windows and update Functions MCP to 1.6.0

[dsghi]

Summary

• add configurable OAuth access-token lifetime and refresh-token replay timeout settings, with deployment guidance in the README
• update Microsoft.Azure.Functions.Worker.Extensions.Mcp from 1.5.0 to 1.6.0
• remove the unused direct ModelContextProtocol 1.3.0 package reference
• update the changelog and v1 package example to match

Why

Allow deployments to tune OAuth token timing for their client retry and refresh behavior while retaining the built-in 10-minute access-token and 5-minute replay defaults. Also keep DevBrain current on the Azure Functions MCP package used by its hosted endpoint.

Validation

• dotnet restore devbrain.slnx — passed
• dotnet test devbrain.slnx --configuration Release --no-restore — 148 passed
• dotnet list devbrain.slnx package --vulnerable --include-transitive --no-restore — no vulnerable packages
• resolved application package graph contains Functions MCP 1.6.0 and no ModelContextProtocol package
• git diff --check — passed