Add SDK and distribution capability map

[clavi-bot]

Summary

• add one capability map for Python, Go, Java, JavaScript/npm, .NET/C#, C++, containers, Helm, custom events, and documentation traffic
• distinguish package-download signals from runtime telemetry
• document opt-outs, failure isolation, and the limits of pixel measurement for text-only crawlers
• link the map from Custom Telemetry and the main navigation

Validation

• git diff --check -- docs/sdk-capability-map.md docs/custom-telemetry.md mkdocs.yml
• MkDocs build completed with the repository requirements in a clean temporary virtual environment
• reviewed the exact public copy with the stop-slop checklist

Remaining risk

• mkdocs build --strict stops on the existing deprecated google_analytics configuration warning; a normal build completes
• the .NET section documents direct HTTP today and does not claim that Scarf publishes an official .NET SDK