Clarify sample maturity tiers and add durable-state reference samples

Problem

The sample catalog does not clearly distinguish quickstart/starter samples from production-ready references, which makes it harder for users to know what can be copied into a real application versus what needs additional production hardening.

Scope

• Document sample maturity tiers and a reusable README template.
• Add durable Azure Blob Storage state starter samples across .NET, Node.js, and Python.
• Add a .NET production-reference support triage sample with managed identity, Key Vault, Blob Storage, health checks, telemetry, Bicep infrastructure, tests, deployment guidance, and runbook.

Validation

• .NET persistent-state build
• .NET production-reference build and tests
• Node persistent-state build
• Python compile check
• Repo lint
• Plugin validation
• Bicep build
• Markdown link/fence validation

Start by surveying the existing sample catalog and README conventions, then map the requested durable-state and production-reference samples across .NET, Node.js, and Python. Done means the maturity guidance, samples, infrastructure, deployment guidance, and runbook are present and all listed build, test, compile, lint, plugin, Bicep, and Markdown validations pass.