Catalog: C# BECs (no-console-writeline)

[DataDave-Dev]

Part of #25 (one language per PR). No code required — a catalog BEC is a single YAML file using the generic forbid check.

Task

Add a ready-to-import C# BEC under src/becwright/becs/:

• no-console-writeline.bec.yaml — forbid Console.WriteLine debugging left in **/*.cs (consider excluding test projects); optionally also Debugger.Break().

How

1. Copy the format from src/becwright/becs/no-debug-go.bec.yaml.
2. Write a real intent and why_it_matters.
3. Use check: "becwright run forbid --pattern '...'" with paths **/*.cs.
4. Add the entry to src/becwright/becs/README.md.

Acceptance criteria

• pytest green (test_catalog_bundles_are_valid covers bundle parsing).
• becwright add no-console-writeline installs it in a scratch repo.

See CONTRIBUTING.md → "Adding a catalog BEC".