ci: add GitHub Actions workflow for Rust, Go, and TypeScript

[Depo-dev]

Add a CI workflow running on push/PR to dev and main.\n\nRust: cargo fmt check, cargo clippy -D warnings, cargo test\nGo: go vet, golangci-lint\nTypeScript: tsc --noEmit\n\nAll three jobs must pass before merge. Workflow lives at .github/workflows/ci.yml.