docs: resolve artifact versions in installation snippets - #120

Summary

• Resolve {{artifactVersion}} in Kotlin fences using the selected release route or the existing snapshot charts_version metadata.
• Leave the placeholder unresolved when snapshot version metadata is missing or invalid.
• Keep existing release documentation and dependency examples unchanged.
• The renderer and Copy button receive the resolved code where the placeholder exists.

Validation

• cd docs-app && npm test (28 passed)
• cd docs-app && npx tsc --noEmit
• cd docs-app && npm run build
• git diff --check