Show SDK validation as separate CI jobs

[bigboateng]

Summary

• show TypeScript, Python, Rust, conformance, examples, and package controls as separate PR jobs
• keep the existing cross-platform Go checks
• keep the protected final validation context and make it depend on every visible job
• use the compact Yield SVG in the README header
• add tests that prevent validation jobs or the compact mark from drifting

Verification

• npm run test:release
• npm test --prefix sdk/typescript
• npm run build --prefix sdk/typescript
• python3 -m unittest discover -s sdk/python -p "test_*.py"
• cargo test --manifest-path sdk/rust/Cargo.toml
• go vet ./...
• go test ./...
• 40/40 workflow evaluations
• 8/8 runtime checks
• GitHub Markdown render inspection
• git diff --check