[DEVT-3004] fix: apply namespace ttl labels during native builds

[vigneshrajsb]

Summary

• route native build namespace setup through the shared namespace create/update method
• let the shared method derive TTL and pull request metadata from build context
• add coverage for native build namespace setup, TTL keep-label behavior, and namespace readiness waits

Validation

• pnpm run lint
• pnpm exec tsc --project tsconfig.server.json --noEmit
• pnpm test
• git diff --check
• local Tilt validation with a public example repository: native build path updated the namespace before service account setup, and the namespace had lfc/ttl-enable=true plus expiration metadata

Notes

• pnpm run ts-check was also tried, but it is currently blocked by existing repo-wide strictness errors outside this change.