docs(kafka): extract inline code examples into snippet files

[hjgraca]

Context

Sub-issue of #794 — extracting inline C# code examples from documentation into standalone snippet files using pymdownx.snippets.

Pattern established by PR #1104 (batch processing + idempotency).

Scope

Doc Path	C# Blocks	Est. Snippet Files	Complexity
docs/utilities/kafka.md	14	2–4	Medium

Branch

docs/extract-kafka-snippets

Acceptance Criteria

• All inline C# code blocks extracted into .cs files under docs/snippets/kafka/
• Language tags normalized to csharp
• hl_lines recalculated
• mkdocs build --strict passes
• Rendered docs visually identical