fix(build): stop stripping zeroconf/_services + add import smoke test

- build-common.sh: remove zeroconf/_services from the strip list.
  zeroconf's compiled Cython _listener.pyd imports from _services
  internally, so stripping it broke `import zeroconf` at runtime with
  ModuleNotFoundError — same class of bug as the numpy.linalg strip.
- build-common.sh: add smoke_test_imports() that imports every top-level
  dependency against the stripped site-packages. Catches "we stripped
  something that was actually needed" regressions at build time instead
  of on a user's machine after install.
- build-dist.sh: wire smoke test into the Linux flow (runs real imports).
- build-dist-windows.sh: cross-build can't load win_amd64 .pyd files with
  the host python, so instead verify that the known-required submodule
  dirs (numpy.linalg/lib/matrixlib/ma, zeroconf._services) exist after
  cleanup. Fails loud if any future strip-rule removes them.

build-dist.sh

@@ -56,6 +56,9 @@ cleanup_site_packages "$SITE_PACKAGES" "so" "so"
 # Pre-compile and strip .py sources (must happen AFTER cleanup)
 compile_and_strip_sources "$SITE_PACKAGES" "python"
 
+# Fail loud if cleanup broke any required import
+smoke_test_imports "$SITE_PACKAGES" "python"
+
 # ── Build frontend ───────────────────────────────────────────
 
 echo "[4/7] Building frontend..."