Summary

• add a dedicated zig build test-integration step for structured backend integration coverage without replacing the existing unit-test gate
• introduce a first integration harness that builds the real nullhub binary, starts it under a temporary home directory, and performs HTTP assertions with Zig's HTTP client
• cover the initial smoke-style routes in structured form: /health, /api/status, and a representative 404 path

Validation

• zig build test -Dembed-ui=false -Dbuild-ui=false --summary all
• zig build test-integration -Dembed-ui=false -Dbuild-ui=false --summary all
• npm --prefix ui ci --no-audit --no-fund
• npm --prefix ui run build
• bash tests/test_e2e.sh
• zig fmt --check src/
• git diff --check

Notes

• this is intentionally the first small harness slice, not the full integration suite; later slices can add instance lifecycle, config mutation, and orchestration flows on top of the same test entrypoint
• the shell smoke test remains in place and unchanged; this adds a structured Zig integration layer rather than replacing the shell coverage immediately