Phase 3: integrated assembled-backend smoke test

Per-module tests in `nodejs-mobile-bare-prebuilds` validate each native addon in isolation. `example/tests/ios/CoreManagerSmokeTest.swift` validates the assembled iOS backend on simulator. What is missing is a focused, fast, per-arch smoke test that validates all six addons loading together inside this module's Node bootstrap, runnable against any target arch in ~3 minutes.

Source plan: `docs/build-architecture-plan.md` §5 Phase 3.

Sketch:

1. `scripts/smoke/` — minimal Node entrypoint that `__loadAddon`s each native module in order and exits 0 with a status line per addon.
2. Tiny Kotlin `SmokeTest` instrumentation test + Swift XCTest target that launches Node with the smoke bundle and captures stdout/stderr.
3. `scripts/smoke.sh [--arch ]` wiring both into one command for emulator and simulator.
4. CI matrix job per target arch.

Exit criterion: one command tells us within ~3 minutes whether the assembled backend loads all six addons on each target arch.

Start with docs/build-architecture-plan.md §5 Phase 3 and compare the existing example/tests/ios/CoreManagerSmokeTest.swift. Trace this module’s Node bootstrap and the six addon entry points, then plan the scripts/smoke/ entrypoint, Kotlin and Swift test launchers, and scripts/smoke.sh wiring. Done means one command reports whether all six addons load for each target architecture within about three minutes.